Revisiting five decades of 234Th data: a comprehensive global oceanic compilation
We present here a global oceanic compilation of 234Th measurements that collects results from researchers and laboratories over a period exceeding 50 years. The origin of the 234Th sampling in the ocean goes back to 1967, when Bhat et al. (1969) initially studied 234Th distribution relative to its parent 238U in the Indian Ocean. However, it was the seminal work of Buesseler et al. (1992) – which proposed an empirical method to estimate export fluxes from 234Th distributions – that drove the extensive use of the 234Th–238U radioactive pair to evaluate the organic carbon export out of the surface ocean by means of the biological carbon pump. Since then, a large number of 234Th depth profiles have been collected using a variety of sampling instruments and strategies that have changed during the past 50 years. The present compilation is made of a total 223 data sets: 214 from studies published in either articles in refereed journals, PhD theses, or repositories, as well as 9 unpublished data sets. The data were compiled from over 5000 locations spanning all the oceans for total 234Th profiles, dissolved and particulate 234Th activity concentrations (in dpm L−1), and POC:234Th ratios (in µmol dpm−1) from both sediment traps and filtration methods. A total of 379 oceanographic expeditions and more than 56 600 234Th data points have been gathered in a single open-access, long-term, and dynamic repository. This paper introduces the dataset along with informative and descriptive graphics. Appropriate metadata have been compiled, including geographic location, date, and sample depth, among others. When available, we also include water temperature, salinity, 238U data (over 18 200 data points), and particulate organic nitrogen data. Data source and method information (including 238U and 234Th) is also detailed along with valuable information for future data analysis such as bloom stage and steady-/non-steady-state conditions at the sampling moment. The data are archived on the PANGAEA repository, with the dataset DOI https://doi.org/10.1594/PANGAEA.918125 (Ceballos-Romero et al., 2021). This provides a valuable resource to better understand and quantify how the contemporary oceanic carbon uptake functions and how it will change in future.
For several decades, radioactive tracers have been used to gain a better understanding of different oceanographic processes. In the context of the biological carbon pump (BCP) (Eppley and Peterson, 1979; Volk and Hoffert, 1985), radionuclides such as 210Po and thorium isotopes are extensively used to study the various physical, chemical, or biological processes involved in the particle export and flux attenuation in the oceans (Cochran and Masqué, 2003). Radionuclides are characterized by a unique property: their half-lives, which account for the time it takes for one-half of the atoms of a radioactive element to undergo radioactive decay and thus transform into a different isotope. Half-lives are not affected by temperature, physical or chemical state, or any other influence. As a result, the concentration of naturally occurring radioactive elements varies over time at well-characterized decay and production rates. Observations of radionuclides' distributions in the water column, in time and space, provide valuable insights into the presence and rates of ocean processes on spatial scales from local to basin-wide and timescales of days to millennia depending on the radionuclide employed.
The naturally occurring radioisotope 234Th has been commonly used to understand natural aquatic processes in four major areas: particle cycling, horizontal transport, sediment dynamics, and vertical transport (Waples et al., 2006). 234Th has been collected by a variety of sampling procedures since its initial use by Bhat et al. (1969). 234Th chemistry dictates that it is adsorbed onto particle surfaces and is effectively scavenged from the dissolved water phase. Hence, when biological activity is high, 234Th is removed from the surface ocean and transported downward by the sinking particles, thereby generating a deficit relative to its soluble or “conservative” parent 238U. This deficit can be used to calculate the downward flux of 234Th. An excess in 234Th activity – i.e. a daughter concentration higher than the parent one – is attributed to fragmentation processes that result in the conversion of sinking to non-sinking particles, generically termed “remineralization” (Maiti et al., 2010). Due to its short half-life of T d (decay constant: d−1; mean lifetime: τ=34.8 d) and its particle reactivity in seawater, it is suitable to trace processes occurring in the upper ocean on timescales from days to months (Rutgers van der Loeff et al., 2006) or even shorter when there is high scavenging by particles (Turnewitsch et al., 2008) (see Sect. 4.2).
234Th has been an indispensable tool in many oceanographic field expeditions. The most widespread application of the 234Th approach is to estimate the gravitational settling of carbon as particulate organic carbon (POC) out of the surface layer, which results in a downward flux of POC (see, e.g., review by Le Moigne et al., 2013a, and references therein). To a lesser extent, this radionuclide is also used to estimate the downward flux of other elements to the deep ocean, such as particulate inorganic carbon (e.g., Le Moigne et al., 2013b; Wei et al., 2011), biogenic silica (e.g., Buesseler et al., 2005; Lemaitre et al., 2016; Le Moigne et al., 2013b), particulate organic nitrogen (PON) (e.g., Buesseler et al., 1992; Charette and Buesseler, 2000; Murray et al., 1996), or trace metals fluxes (e.g., Black et al., 2018; Lemaitre et al., 2016, 2020; Weinstein and Moran, 2005).
It was in the 1990s that an increasing number of studies for 234Th took place. This increase in use is in part due to a variety of new sampling instruments and strategies that have changed over the years. In 2006, a special issue entitled “Future Applications of 234Th in Aquatic Ecosystems” (FATE; https://www.sciencedirect.com/journal/marine-chemistry/vol/100/issue/3, last access: 1 June 2022) was published in Marine Chemistry with the purpose of thoroughly reviewing the use of 234Th in aquatic systems. Papers included reviews of the applications and future uses of this radiotracer (Benitez-Nelson and Moore, 2006; Waples et al., 2006), discussions on the techniques and methodologies used for 234Th analyses (Rutgers van der Loeff et al., 2006), the impact of POC:234Th ratios and their sampling methodology on POC flux estimates (Buesseler et al., 2006), and 234Th sorption and export models in the water column (Savoye et al., 2006), among other topics. As one of the most actively used tracers in oceanography, Waples et al. (2006) already reported 237 papers dealing with 234Th published in refereed journals. However, after five decades of extensive use, a unique repository of 234Th measurements has never been compiled, and 234Th data remain scattered when not belonging to major sampling programs (see Sect. 4 for details). Therefore, it is valuable to bring together all existing 234Th data, along with appropriate metadata, in one repository to facilitate further use and analysis.
Previous efforts compiling 234Th-based data have been created to access 234Th-derived POC fluxes (see Le Moigne et al., 2013a), total 234Th activity from the surface to 1000 m depth (Le Gland et al., 2019), and, more recently, POC:234Th ratios (see Puigcorbé et al., 2020, and https://doi.org/10.1594/PANGAEA.911424; Puigcorbé, 2019). In contrast, we have compiled the complete results of 234Th measurements in seawater and particles at every depth, location, and time of sampling. The compilation can be found at https://doi.org/10.1594/PANGAEA.918125 (Ceballos-Romero et al., 2021). This article is the report of the compilation, a unique dataset to better understand and quantify how the contemporary oceanic carbon uptake functions and how it will change in future.
The goal of this effort is to serve as a basis for an open-access, long-term, and dynamic oceanic repository of 234Th measurements and valuable metadata to be used in an accessible, easily findable, and inter-operable way that grows from now on from the contribution of other authors involved in 234Th sampling. Moreover, given the great amount of metadata and parameters compiled, the compilation offers multiple ways to use 234Th, even opening the possibility of exploring new applications. For that reason, we have chosen not to compile the derived parameters reported by other authors, such as 234Th downward fluxes or 234Th-derived POC fluxes, but rather provide the data necessary for others to make such analyses, open to the criteria, modeling, and interpretation chosen by each researcher.
2.1 Data organization
We have gathered data sets consisting of 234Th measurements in oceanic waters sampled between 1967 and 2018. The compilation includes a total of 56 631 data points for 234Th activity concentrations (in dpm L−1, referred to as simply 234Th concentrations from now on), distributed as follows: (i) 21 457 for total, (ii) 6591 for dissolved, (iii) 13 977 for particulate 234Th measurements, and (iv) 10 856 and (v) 3750 for POC:234Th and PON:234Th ratios respectively (in µmol dpm−1). Note that when total carbon is provided instead of POC:234Th ratios (such as in, e.g., Owens et al., 2015) this is indicated in the “methods” section of the “metadata” sheet (see Sect. 2.1.1). Additionally, 238U concentrations (18 256 data) and POC (7651 data) and PON (1740 data) concentrations (in µmol L−1) are also reported. POC and PON concentrations are referred to as “CHN” (carbon–hydrogen–nitrogen) in the compilation. We are aware that CHN is not the only analytical method that can be used to determine POC and PON concentrations. An elemental analyzer – isotope ratio mass spectrometer (EA-IRMS) is also widely used for this purpose (see, e.g., studies by Lemaitre et al., 2018, and Planchon et al., 2015), but we have used this notation for the sake of simplicity. Please refer to the original source for the analytical method used to measure these data. Temperature and salinity values are also included when possible, making a total of 5652 values compiled for temperature and 12 721 values for salinity. When fields are missing for a given record, the data are entered as “−999”.
The data have been extracted from a total of 219 different studies published in refereed journals between 1969 and 2020, 5 PhD dissertations, 9 data sets accessible in four different public repositories, and 9 unpublished ones directly provided by authors (listed in Table 1) spanning all oceanic regions (Fig. 1a) and compiled in a total of 223 data sets. The data repositories include the following: (1) BCO-DMO® (Biological and Chemical Oceanography Data Management Office; https://www.bco-dmo.org/, last access: 1 June 2022), (2) DARWIN® (Data and Sample Research System for Whole Cruise Information in JAMSTEC; https://www.jamstec.go.jp/e/database/, last access: 1 June 2022), (3) EDI Data Portal® (Environmental Data initiative; https://portal.edirepository.org/nis/home.jsp, last access: 1 June 2022), and (4) PANGAEA® (https://www.pangaea.de/, last access 1 June 2022). Additionally, many of the data corresponding to published GEOTRACES ®(https://www.geotraces.org/, last access: 1 June 2022) cruises can be found on the GEOTRACES website (see the most recent version of its intermediate data product released in 2021; GEOTRACES Intermediate Data Product Group, 2021).
Each data set is univocally identified with a unique integer record ID number (denoted as “Reference_USE”) and consists of two tables: (i) the “metadata” and (ii) the “data”.
2.1.1 Metadata sheet
The metadata table is a list of the data's origin in its broadest sense at a glance. It contains information structured in six categories: (1) “REFERENCE_USE”, (2) “INFO”, (3) “DATA”, (4) “METHODS”, (5) “ADDITIONAL_DATA”, and (6) “DATA_SOURCE”. The full list of metadata included in each dataset and a brief description of the table fields can be found in the Supplement (see Table S1).
There are data from 379 cruises, covering 5134 locations spanning across all oceanic regions (Fig. 1a). Some stations were part of cruise transects, whereas others were part of small-scale surveys or reoccupation of the same location at different seasons and years. In all cases, sampling region and period – including bloom stage at the sampling moment when indicated by the authors – are given as metadata as part of the “INFO” section, in which a total of 17 fields are reported (see Table S1).
Information such as the project name, when sampling took place within an observational program, cruise name, leg details, research vessel, and chief scientist is indicated. A summary of the sampling period, the maximum and minimum latitude and longitude of the region surveyed, and the maximum depth sampled for 234Th is also provided. When available, for the sake of a better interpretation of the data for the accurate POC flux assessment, the stage of the bloom has also been included (categorized as “bloom”, “pre-bloom”, “post-bloom”, and “no bloom”), as recommended by, for example, Ceballos-Romero et al. (2016, 2018). Note that we do not assess the bloom stage, but instead we include the information as indicated by the original authors when provided. To distinguish between the periods before and after the peak in primary production, we identify “development of the bloom” and similar expressions as pre-bloom stage and “decline of the bloom” and similar as post-bloom phase. Only when bloom or non-bloom conditions are stated by authors have we assigned these phases. When none of these stages are referenced, no information is included (noted as “−999”). We acknowledge there could be issues on the way the different authors have decided if the conditions were non-bloom, pre-bloom, bloom, or post-bloom over the different years that are out of the scope of this compilation and were not evaluated. We plan to address this gap in the compilation in future versions of it (see Sect. 5).
The “DATA” section provides information of the data set contents at a glance with YES/NO indicators to the basic data of 238U, 234Th (total, dissolved, and particulate phases), and POC (PON):234Th ratios. The fraction size details and the number of total stations and samples are also reported. A total of 13 parameters are detailed in this section.
The “METHODS” section is intended to provide useful interpretive information regarding how the sampling and/or measurements were accomplished at a glance. It provides basic information about (i) 238U determination: whether it was directly measured or salinity-derived, in which case the salinity relationship employed is specified; (ii) total 234Th sampling and radiochemical purification methods; sampling methods for the (iii) dissolved and (iv) particulate 234Th phases; and (v) the modeling approach followed when 234Th data were used to estimate POC fluxes (i.e., the assumption of steady- (SS) or non-steady-state (NSS) conditions). A final space for comments of any kind is included in this section.
The potential of 234Th data increases when combined with methods that account for export episodes over different timeframes of a bloom period, such as 210Po–210Pb, or sediment traps (see, e.g., Ceballos-Romero et al., 2016). For that reason, we included information regarding the availability of some other techniques when combined with 234Th sampling in the “ADDITIONAL_DATA” section. Additional data of interest are specified with YES/NO indicators for the cases of (i) 234Th underway sampling, (ii) sediment trap deployments, (iii) 234Th being paired with 210Pb–210Po disequilibrium sampling, and (iv) CHN data. Note that this section is merely intended as being informative of the sampling methods used complementarily to the 234Th technique. Both 234Th underway data and POC:234Th and PON:234Th ratios from sediment traps are reported when available. However, 210Pb–210Po concentrations are not compiled in this dataset. The availability of these data is indicated as reported by authors. We have only consulted publications and cruise reports when accessible to gather information for these metadata, so we acknowledge that information as to the existence of these data might be missing. We therefore recommend using them cautiously when stated “NO (available)” but fully trust it when stated “YES”. To report an update to the metadata or an error in the data compiled, we encourage authors to contact us, and changes will be included in future versions of the compilation (see Sect. 5).
It is also worth mentioning here that the amount of data that could be additionally reported in the compilation is very extensive due to the wide applicability that has been shown for 234Th throughout the years (see, e.g., review by Waples et al., 2006). The inclusion of new parameters in a future version of the compilation will be discussed in Sect. 5 as part of our assessment of steps towards improving the global data set.
Finally, several details regarding the data source are included in the eight fields specified in the “DATA_SOURCE” section, including a YES/NO indicator for the publication date. The data owners are always clearly indicated by the first author(s) of the publication or data set. In the case of data published in research articles, the journal and the publishing year are indicated, while in the case of unpublished data obtained from personal communication (as is the case for nine datasets), “np” (for non-published) is given in the journal information, and no data are provided as publication year (indicated as “−999”). If data had been assigned a digital object identifier (DOI), this is included in DOI/others. When no DOI is available, the data URL source – either database or publication links – is included instead. Other URL sources or personal communication from data sources is keyed by the text variable “data_resource” in the “metadata” table, when available.
Most of the measurements were obtained from publications. In these cases, if the data were transcribed from tables, the table number is also given as “data localization”. If data were only available graphically, a computer program to digitize the data from plots was used (WebDigitizer, https://automeris.io/WebPlotDigitizer/, last access: 1 June 2022), and the figure number is also given. In the rare cases in which data were not accessible through any of these procedures, the authors were directly contacted for data. For those cases, the author(s) contacted is (are) indicated in the “data localization” field.
Finally, a space for further links or information of interest is provided under the text variable “other DOI/resources”. In the few cases that the same data were reported in another publication (e.g., Murray et al., 1996, Dunne et al., 1997, and Murray et al., 2005, reported the same data from the U.S. JGOFS (Joint Global Ocean Flux Study) program during 1992 in the equatorial Pacific), it was indicated under this text variable.
2.1.2 “Data” sheet
The “data” table is the data set core and contains all the data detailed above (more details in Table S2).
Each data point is accompanied by cruise and station IDs, location – latitude, longitude, depth, and additionally bottom depth when available – and sampling date – including month–date–year and day-of-year (DOY) formats. All 234Th (total, dissolved, and particulate) concentrations were converted to disintegration per minute per liter (dpm L−1; density 1027 kg m−3) if not already reported in these units. POC:234Th and PON:234Th ratios are given in micromoles per disintegration per minute (µmol dpm−1) and include samplings with sediment traps and filtration methods, in which we report (i) bottles – Go-Flo and Niskin types – (ii) filtration systems, (iii) SPLITT (split flow-thin cell fractionation), and (iv) (large or small volume) in situ pumps for either the entire particulate fraction or two sizes classes (preferably 1–53 and >53 µm) when available. These size classes were chosen largely based on results of Bishop et al. (1977), Clegg and Whitfield (1990), and others, who assumed that the >53 µm size class was responsible for most of the mass flux into traps. Other cutoffs of 51 or 70 µm and other size classes are found and are noted when different than 53 µm. The particles' sampling method – categorized as “method 1” (for filtration methods) and “method 2” (for sediment traps) – and size fractions – categorized as “small” or “large” – are specified as part of the data. Total, particulate, and sediment trap 234Th sampling depths are separately indicated. When reported, water temperature, salinity, and 238U measurements are included. Moreover, if accessible, POC and PON concentrations (“CHN” data in µmol L−1) are included.
In all cases we assume that the originating authors and editors have undertaken steps necessary to control data quality. Measurement uncertainties in the data points are compiled as provided by the original authors (e.g., “uncert_total_234Th”). Please refer to the original source for whether data uncertainty includes only the 1-sigma counting error or other factors, such as uncertainty in volumes, detector efficiency, background, etc.
2.2 Data formats and availability
The data are archived on the PANGAEA repository, with the data set's DOI https://doi.org/10.1594/PANGAEA.918125 (Ceballos-Romero et al., 2021). The data table is available for download either as a unique merged file containing all data sets and metadata or as individual Excel files.
Moreover, the template followed to compile the data set (including the “metadata” and “data” tables) along with instructions to fill in this template is available in PANGAEA for any author who wants to either review a data set, complement a data set included in this compilation, or contribute to its extension with a new data set. We strongly encourage authors to contact us to submit suggestions or requests to amend the data sets compiled.
In this article, we aim at providing a broad overview of the character of the data sets to be used for different purposes in future studies. We therefore provide several graphics to indicate the scope and nature of the data compiled. These include maps of sampling locations (Fig. 1a) and time histories of analyses per year for 234Th measurements (Fig. 2), among others. Additionally, a summary table with the most remarkable metadata is also provided at https://doi.org/10.1594/PANGAEA.918125 (in the “Download data” section and “View dataset as HTML” option). Note that the compilation here presented does not overlap with the previous compilation by Le Moigne et al. (2013a), in which 234Th flux, POC:234Th ratios, and234Th-derived POC fluxes were gathered together along with primary production data mostly for a fixed depth of 100 or 150 m only.
3.1 General overview
In this section we give an overview of the compilation and some important aspects for its use. In Sect. 4 we present a historical review of the 50 years of the 234Th studies. In Sect. 5 we discuss steps towards improving the global data set, and in Sect. 6 we briefly suggest some future perspectives and applications for the data sets.
The sampling locations shown in Fig. 1a are dominated by cruise tracks mostly in the Northern Hemisphere (NH) (Fig. S1), although there are also a few locations in the Southern Hemisphere (SH) with significant repeated sampling, especially in the Southern Ocean (Fig. 1b). Over a total of 379 cruises compiled, 294 took place exclusively in the NH (78 %), only 53 in the SH (14 %), and a total of 32 (8 %) crossed the Equator and sampled locations in both hemispheres.
* Observations at Station Papa (former Ocean Station Peter and referred to as OSP or Ocean Station “P”) started in 1949, although the larger surveys became a focus of activities in support of JGOFS during the 1990s (Freeland, 2007).
Many of these expeditions were carried out in the framework of larger research programs. For those cases, this information has been included as metadata in the compilation. During these 50 years of 234Th data, we have selected a total of 13 ocean programs in which 234Th has been widely applied and which have provided invaluable knowledge to the 234Th approach (see Table 2). Note that these programs have been chosen with the purpose of providing a wide global distribution and international representation of 234Th from different institutions and organizations. A total of 68 (30 %) of the data sets were collected during surveys as part of one of these 13 programs. Additionally, for cruises belonging to specific projects or experiments, this information has also been reported.
Sampling locations for 234Th also include a number of long-term, high-frequency observations at fixed locations in the open ocean, referred to as (long-term) time-series stations (TSSs) from now on. These stations offer a crucial observational strategy for capturing the dynamic temporal changes in ocean conditions and biogeochemical processes at the seasonal and decadal scale. Moreover, it allows for investigating short-term episodic events usually unaccounted for by oceanographic cruises. A great number of TSSs that are either operational, registered (for future operation), inactive, or closed are spread across the globe (source: https://www.ocean-ops.org, last access: 1 June 2022). We have acknowledged the importance of sampling at these TSSs by identifying matches with 234Th sampling locations (see Fig. 1c). Coincidences between locations with 234Th data available and the position of a TSS station have been reported in the metadata section with the label “time series” in the “number of stations” field. Note that this should not be mistaken with repeated sampling of a location during a cruise, which has also been acknowledged with the label “reoccupied” in the same field. A total of 98 data sets (44 %) reported samplings on at least one TSS location, while only 33 (15 %) reoccupied the sampling site. The most frequent TSS sampling sites found in the compilation include the Bermuda Atlantic Time Series Study (BATS; 31.50∘ N, 64.10∘ W; http://bats.bios.edu/, last access: 1 June 2022), the Hawaii Ocean Time series (HOT; 22.45∘ N, 158∘ W; https://hahana.soest.hawaii.edu/hot/hot_jgofs.html, last access: 1 June 2022) at station ALOHA, and the Dynamics of Atmospheric Fluxes in the MEDiterranean sea (DYFAMED; 43.42∘ N, 7.87∘ E; http://www.obs-vlfr.fr/cd_rom_dmtt/sodyf_main.htm, last access: 1 June 2022) – all of them part of JGOFS. Some other relevant ones such as the South East Asia Time-series Study (SEATS; 18.00∘ N, 166.00∘ E; https://www.odb.ntu.edu.tw/seatsen/#:~:text=The%20SEATS%20time%2Dseries%20station,Arctic%20Sea%20is%20the%20largest, last access: 1 June 2022), also from JGOFS, the Palmer Antarctica and California Current Ecosystem Long-Term Ecological Research projects (PAL-LTER (https://pal.lternet.edu/, last access: 1 June 2022) and CCE-LTER (https://cce.lternet.edu/, last access: 1 June 2022) respectively), or the Porcupine Abyssal Plain (PAP; 49.00∘ N, 16.50∘ W; https://projects.noc.ac.uk/pap/, last access: 1 June 2022) site sustained observatories were also sampled, among others (Fig. 1c). More details of the history of these locations repeatedly sampled for 234Th will be given in forthcoming sections.
Over time, the interdisciplinary scope of the studies and the number of techniques and parameters simultaneously assessed have gradually evolved. Field surveys have changed not only in terms of number but also in terms of strategy (e.g., duration, spatial resolution, and repeated occupation of the same site). This has influenced not only the number of data points measured – with a sustained increasing trend – but also the type of 234Th data reported (i.e., total, dissolved, and particulate phases and POC(PON):234Th ratios). Similarly, it has driven changes in the number of 234Th studies published. We have identified three key indicators of these inflection points. In the 1990s the number of 234Th studies dramatically increased after the publication of the first empirical routine method to estimate downward POC fluxes in the ocean by Buesseler et al. (1992). Another tipping point took place in the 2000s likely due to significant improvements in the 234Th methodology derived from the introduction of the small-volume technique (C. R. Benitez-Nelson et al., 2001). Moreover, it is important to note that it was in the late 2000s when Yool et al. (2007) proved that other empirical methods such as the 15∘ N new production techniques (f ratio) largely overestimated the efficiency and magnitude of the carbon export. Finally, a later shift took place with the change in the way an ocean is currently explored and the expansion of applications to trace metals and isotopes introduced by GEOTRACES, whose first 234Th-related publication was released in 2010 with the first version of the Cookbook: “Sampling and Sample-handling Protocols for GEOTRACES Cruises” by Cutter et al. (2010). More details of these milestones and the consequences they brought to the 234Th technique will be discussed in Sect. 4.
The overall temporal evolution of 234Th measurements is depicted in Fig. 2. Figure 2a shows the annual number of field expeditions including 234Th measurements per sampling year between the initial measurements from 1967 to 2018, separated by oceans. Figure 2b shows the equivalent figure for the annual oceanic distribution of 234Th data points, and Fig. 2c shows the histogram of 234Th data points sampled since 1967 separated by data type. Additionally, the time distribution of annual 234Th publications (in either refereed journals, PhD theses, or repositories) since the first reported publication in 1969 separated by oceans is shown in Fig. S2.
Despite the fact that the first 234Th study took place in the Indian Ocean in 1967, this ocean along with the waters from the Arctic Ocean, visited for the first time in 1994, is the least surveyed one during this 50-year compilation (Fig. 2a). The Atlantic and Pacific oceans dominate the sampling locations, followed by the Southern Ocean to a much lesser extent. Field expeditions to the Pacific Ocean started in 1970, in 1977 to the Atlantic, and in 1987 to the Southern Ocean. Other locations include several rivers, lakes, and bays (see Fig. 1a).
During the 1960s–1970s, expeditions including 234Th measurements were scarce, with the total number of annual samplings never exceeding five. It was in the 1990s when the number of 234Th samplings started to dramatically increase, with an average number of annual expeditions of 15. In the subsequent years, a great number of cruises took place, with an average of 10 per year during the last two decades. However, the annual number of dedicated cruises is not representative of the number of 234Th points reported by year. In the past, the number of cruises including 234Th measurements greatly increased over time and so did the number of data points, while more recently, a larger amount of data (Fig. S2) is reported from a reduced number of cruises (see Fig. 2a).
There are several remarkable peaks in the annual record of 234Th data points which are related to dedicated carbon export programs and experiments that will be detailed in the next sections. A delay of about 3–4 years relative to sampling is commonly observed for the publication of these 234Th data and derived results, which started in 1969 (see Fig. S2). Namely, as shown in Fig. 2b, peaks in the number of data points stand out in the following years: (i) 1992, when the JGOFS Equatorial Pacific process study took place, published by several groups in 1995–1997 (Bacon et al., 1996; Buesseler et al., 1995; Dunne et al., 1997; Murray et al., 1996) and extended in 2001 with the publication of POC:234Th ratios from sediment trap results by Hernes et al. (2001); (ii) 1997, when the JGOFS Southern Ocean study and the Arctic expedition ARK XIII/2 were carried out, published by Buesseler et al. (2001a) and Rutgers van der Loeff et al., (2002b) respectively; (iii) 2004, when several intense expeditions took place, with VERTIGO voyages as the most productive ones in terms of data contribution, published by Buesseler et al. (2009) and Lamborg et al. (2008); the Shelf–Basin Interactions (SBI; https://arctic.cbl.umces.edu/sbi/web-content/, last access: 1 June 2022) Phase II field program, published in 2007 by several authors (Lalande et al., 2007; Lepore et al., 2007; Lepore and Moran, 2007); the EDDIES project, synthesized by Buesseler et al. (2008); and the CROZEX project available in Morris et al. (2007); (iv) 2010, when a total of 17 cruises took place, with the Southern Ocean cruises (Owens, 2013) as the most intense ones in terms of number of 234Th samples per day, as well as several GEOTRACES section cruises (two cruises to the South Atlantic Ocean (GA10, UK) published by Le Moigne et al. (2014), three cruises to the Atlantic Ocean (GA03 (legs 1 and 2), USA, and GA02 (leg 3), Netherlands) published by Owens et al. (2015), and two cruises in the Atlantic Ocean from 64∘ N to the Equator (GA02 (legs 1 and 2), Netherlands) published by Puigcorbé et al. (2017a); and finally (v) 2018, when two GEOTRACES cruises were carried out in the Pacific Ocean (GP15 (leg 1), USA, Pacific Meridional Transect, and GP15 (leg 2), USA) unpublished until now but which have been reported in this compilation by personal communication with Jennifer Kenyon (2020), as well as the first field expedition of the EXPORTS program taking place (published by Buesseler et al., 2020).
3.2 Total, particulate, and dissolved 234Th
Changes in the type of 234Th data measured during field expeditions are depicted in Fig. 2c. While within the first years of the 234Th technique, authors focused on the total, dissolved, and particulate phases mainly for the study of the scavenging of 234Th and the partitioning of Th species between phases (see, e.g., Bacon and Anderson, 1982, McKee et al., 1986, Murray et al., 1989, and Nozaki et al., 1981), in the 1990s the broader potential of 234Th and its application as a tracer for particle dynamics and export fluxes became evident, which drove the inclusion of sampling strategies for the determination of POC(PON):234Th ratios. Given the reduced annual number of data points in the 1970s–1980s, in comparison to subsequent years, it is difficult to perceive the contribution of each data type to the total number of data points within the first years of study. A detailed review of the evolution of 234Th data available through years in the framework of the mentioned milestones is given in Sect. 4.
In summary, total 234Th is almost always reported by all authors either by direct measurement or determined as the sum of the dissolved and particulate phases. It is worth mentioning that the distinction between dissolved and particulate is operational. Dissolved and particulate species have traditionally been discriminated by filter sizes, typically of 0.2–1 µm pore size (Moran and Buesseler, 1993), with the submicron colloidal matter – nanometer to submicrometer size range ∼0.001–1 µm (Stumm, 1977) – included in the dissolved phase. Note that colloidal size ranges have not been included in the compilation but are indicated in the metadata section when available. The 0.7 µm cutoff for the dissolved particulate fractions is very frequent since it is the nominal pore size of the Whatman glass microfiber filters (so-called GF/F) that have been historically used to collect particulate 234Th (Buesseler et al., 1998). Nonetheless, the use of 1 µm pore size quartz microfiber (QMA) filters has been more common since the early 2000s due to their lower radioactivity blank with direct beta counting (e.g., Buesseler et al., 2001a). A general view of the 234Th particulate data compiled is provided in Fig. S3, which shows the locations with 234Th concentrations sampled on either small (generally from 0.7–1 to 53–70 µm), large (>53 or >70 µm), or both size fractions. An overall 75 % of the studies compiled reported particulate 234Th concentrations, and more than half of them (56 %) reported data in two size fractions.
In a reduced number of studies, 234Th concentrations were determined as a single vertically integrated sample, normally between 0 and 100 m depth (i.e., Buesseler et al., 1998, 1994, 1995; Charette et al., 1999; Charette and Buesseler, 2000; Cochran et al., 2000; Evangeliou et al., 2011; Hall et al., 2000; Ma et al., 2005; Maiti et al., 2008; Schmidt et al., 2002b). This sampling approach was deliberately done to reduce sample numbers yet maximize the number of locations sampled at a time when at sea analyses were more difficult. This has also been indicated in both the metadata and data sections in each individual spreadsheet with the code number “−555” in the depth column (see Tables S1 and S2).
A total of 66 % of the studies reported POC:234Th ratios measured with some of the filtration methods (described in detail in Sect. 2.1.2), while only ∼16 % reported PON:234Th ratios. In ∼40 % of the studies compiled, POC(PON):234Th ratios collected with sediment traps were reported from a great variety of trap designs: indented rotating sphere (IRS), surface-tethered, free-floating, bottom-moored, automated, cylindrical, VERTEX-style, U-type, CLAP-type, RESPIRE-type, free-drifting Lagrangian sediment traps (LSTs), high-frequency flux (HFF) standard drifting particle interceptor traps (PITSs), and, more recently, neutrally buoyant sediment traps (NBSTs) and particle export measurement using a Lagrangian (PELAGRA) trap. An overview of POC:234Th data compiled is shown in Fig. S4.
Note that a specific, more detailed compilation of global POC:234Th ratios in the ocean has been recently published by Puigcorbé et al. (2020) (archived in the data repository PANGAEA® under https://doi.org/10.1594/PANGAEA.911424) with the purpose of elucidating the spatial, temporal, and depth variations in this crucial parameter. The authors present a database of 9318 measurements sampled on three size fractions (, ∼1–50, µm) collected with in situ pumps, bottles, and sinking particles collected in sediment traps from the surface down to >5500 m. Our compilation includes the studies gathered in Puigcorbé et al. (2020) and expands the data set with a total of 10 851 POC:234Th ratios.
3.3 238U measurements
Finally, in order to allow the assessment of POC fluxes, 238U concentrations have also been included. This is generally either reported by authors by direct measurement or, most commonly, derived from salinity data by applying one of the 238U–salinity relationships available. From the studies compiled, we have identified a total of 11 salinity–238U relationships published in journal articles, chronologically ordered as follows: (i) Ku et al. (1977); (ii) Broecker and Peng (1982), (iii) Coale and Bruland (1985), (iv) Chen et al. (1986), (v) Andersson et al. (1995), (vi) Delanghe et al. (2002), (vii) Rutgers van der Loeff et al. (2006), (viii) Pates and Muir (2007), (ix) Owens et al. (2011), (x) Not et al. (2012), and (xi) Martin et al. (2013), along with some other relationships also frequently used such as 2.4 dpm kg−1 at salinity 35, 0.06813× salinity ‰, or 0.07097× salinity ‰. The most extended 238U–salinity relationships are the ones given by Ku et al. (1977) ( salinity), Chen et al. (1986) ( salinity), and, more recently, by Owens et al. (2011) (AU (±0.047) = 0.0786× salinity − 0.315).
The compilation covers a temporal range of five decades. The temporal distribution of oceanic 234Th measurements begins in 1969 to measure its distribution in the hydrologic cycle (Bhat et al., 1969) and extends up to the present day as an indispensable tool in oceanographic expeditions. We consider that it was not the passing of years but rather the publication of seminal key studies that delineates the progression of 234Th studies. For this reason, we have divided the 234Th technique time history in four well-distinguished eras, marked by four publications, summarized in Fig. 3. Therefore, it is the publication date rather than the sampling date that determines the era to which a dataset belongs. Note that this definition of eras by publications rather than sampling dates implies that cruises that took place within the time frame of a previous era are included in the era of their publication. Delays of up to decades between sampling and publication can sometimes be found. In addition, in the case that a later publication (from a later era) used data from a cruise that was already published in a previous era, that publication is included in the earlier era despite the year of the actual publication.
4.1 Era 1: “The Old Man and the Sea”
1969–1991: the beginning of 234Th as tracer of particle scavenging.
“Now is no time to think of what you do not have. Think of what you can do with what there is.”
– Ernest Hemingway, The Old Man and the Sea.
The first era within the 234Th timeline was initiated by the study of Bhat et al. (1969), in which a total of six profiles of total 234Th:238U ratios in depths up to 250 m were collected on board the USC and GSS Oceanographer during 1967 at several sampling sites in the Indian Ocean to study scavenging processes. Polyvinyl chloride (PVC) tube samplers of 30 L capacity designed by Shale J. Niskin (Niskin, 1962) were used.
It was in the framework of the GEOSECS (the GEochemical Ocean SECtions Study) project (http://iridl.ldeo.columbia.edu/SOURCES/.GEOSECS/, last access: 6 June 2022) that the concept of scavenging by particles really emerged, especially for the open ocean. The initiation of global ocean chemistry, hydrographic, and tracer survey efforts took place within this era, especially with GEOSECS, which was fundamentally different in style and scale than anything before. This project provided the first comprehensive data set for the distribution of chemical species in the world ocean between 1972 and 1978 (Moore, 1984). In 1977, the seminal work of Turekian introduced the concept of the “great particle conspiracy” to denote the fact that dissolved elements are, to a certain extent, particle reactive. All this contributed to further increase 234Th research and pointed towards the second era of the 234Th technique.
The pioneering study by Bhat and collaborators was expanded by many other investigations (e.g., Kaufman et al., 1981; Knauss et al., 1978; Lee et al., 1991; Matsumoto, 1975; Tanaka et al., 1983; Tsunogai et al., 1986). All these studies analyzed total 234Th (both particulate and soluble forms) giving different interpretations to the total 234Th vertical distribution. Bhat et al. (1969) assumed that essentially all 234Th in seawater was in particulate form, whereas Matsumoto (1975) assumed particulate 234Th to be an insignificant part of the total 234Th. This led to a not very informative scavenging model being applied to the surface euphotic layer until the sampling of profiles of 234Th in both dissolved and particulate form was introduced. The analysis of particulate 234Th was incorporated by Krishnaswami et al. (1976) during a survey in the Pacific Ocean. Several authors sampled both total and particulate 234Th concentrations (e.g., McKee et al., 1984; Minagawa and Tsunogai, 1980), while the sampling of the 234Th dissolved phase was initiated by Santschi et al. (1979). From 1979 on, many studies sampled both dissolved and particulate phases (see, e.g., Coale and Bruland, 1985, McKee et al., 1984, and Wei and Murray, 1991).
Initially in this era, little attention was given to 234Th in comparison to 228Th and 230Th for studying scavenging processes in the open ocean (Broecker and Peng, 1982). It was only later, with the influential study of Coale and Bruland (1985), that the role of 234Th as a tracer of short-term particle dynamics was really highlighted. In that study several profiles of 234Th in both dissolved and particulate form were presented and used to elucidate the partitioning of 234Th between these phases. This allowed the authors to demonstrate that this radioisotope is an ideal particle reactive tracer for studying the scavenging of thorium from surface waters.
In fact, a series of papers by Coale and Bruland in the mid-1980s (Bruland and Coale, 1986; Coale and Bruland, 1985, 1987) were key for establishing the baseline for future 234Th studies that would use 234Th as a proxy for POC fluxes in the next era. The authors discovered that the 238U–234Th disequilibrium is a direct tracer of the rates of sinking particles from the upper ocean, which led to the acknowledgment of the relevance of the downward 234Th flux. Previously, in a 1-year time-series study, Tanaka et al. (1983) found large variations in the total 234Th concentrations, with the minimum in 234Th inventory coinciding with the early spring bloom, which they proposed was related to biological activity in the surface waters. It was within this context that Eppley (1989) proposed that, if 234Th is scavenged by biogenic particles, 234Th could be used as a tracer of export production.
The “Coale and Bruland papers” were followed by many other investigators (e.g., Bacon and Rutgers van der Loeff, 1989; Huh and Beasley, 1987; Kershaw and Young, 1988; Murray et al., 1989; Rutgers van der Loeff and Berger, 1991; Schmidt et al., 1990; Wei and Murray, 1991).
A series of milestones have been identified as the most remarkable of this era, which are summarized as follows:
1969: initial measurement of total 234Th and introduction of the co-precipitation of 234Th with Fe(OH)3 (Bhat et al., 1969);
1972: beginning of GEOSECS program, which would be prolonged until 1978 and transform the field of chemical oceanography as it existed at that time by exploiting new technologies available then (see synthesis of results by Broecker and Peng, 1982);
1977: introduction of the concept of the “great particle conspiracy” by Turekian (1977);
1979: initial analysis of particulate and dissolved 234Th in the Narragansett Bay (Santschi et al., 1979);
beginning of the Joint Global Ocean Flux Study (JGOFS) program, which grew out of the recommendations of a National Academy of Sciences workshop and would last until 2003;
introduction of the MnO2-impregnated filter cartridge technique (Mann et al., 1984), used with in situ pumps;
1985: initial analysis of particulate and dissolved 234Th in open ocean and link between biological processes and 234Th deficits clearly demonstrated (Bruland and Coale, 1986; Coale and Bruland, 1985, 1987);
1987: one TSS project established in the framework of the French MOOSE project (Mediterranean Ocean Observing System for the Environment) and the JGOFS-France program: DYFAMED: Dynamics of Atmospheric Fluxes in the MEDiterranean sea (43.42∘ N, 7.87∘ E);
1988: beginning of JGOFS field work with the establishment of two TSS projects:
BATS: the Bermuda Atlantic Time-series Station in the Atlantic Ocean (31.50∘ N, 64.10∘ W), and
HOT: Hawaii Ocean Time-series in the Pacific Ocean at Station ALOHA: A Long-term Oligotrophic Habitat Assessment (22.45∘ N, 158∘ W);
1989: 234Th proposed to trace export production (Eppley, 1989);
1990: one TSS project established in the frame of JGOFS program: OSP – Station PAPA Ocean Weather Station “P” in the Pacific Ocean (50.1∘ N, 144.9∘ W) – note that observations at Station Papa (formerly Ocean Station Peter and referred to as OSP or Ocean Station “P”) started in 1949, although the larger surveys became a focus of activities in support of JGOFS during the 1990s (Freeland, 2007).
There exist two distinct radioanalytical methods for the 234Th extraction and purification from water samples that were initiated during this era: (i) the co-precipitation of 234Th with Fe(OH)3, proposed by Bhat et al. (1969), and (ii) the scavenging of this nuclide onto MnO2 cartridges, introduced by Mann et al. (1984). A thorough review of these techniques can be found in Rutgers van der Loeff et al. (2006). Briefly, for the Fe(OH)3 technique, 20–30 L seawater samples are treated and beta-counted. The addition of Fe carrier forms a precipitate that removes Th (and other elements) from solutions, so ion exchange purification procedures are required (at sea or quickly after return to shore) to separate 234Th from its parent and other potential beta emitters. For the MnO2 cartridge technique, seawater is sequentially pumped through filters and two MnO2 impregnated cartridges connected in series to scavenge dissolved Th isotopes. This technique was often used with large volume samples (102–104 L), needed primarily for 228Th, 230Th, and 232Th analyses, which required large amounts of ship time given the use of in situ pumps for filtration, limiting the spatial coverage of the 234Th profiles. MnO2 cartridges do not adsorb appreciable 238U, which is another advantage as ingrowth after sampling from 238U can be neglected. The large samples represented by a MnO2 cartridge also allowed for direct gamma counting, thus eliminating the need for laborious radiochemical purification.
A wide variety of methods were used to sample the different 234Th phases within era 1. For the total phase, PVC tubes and Van Dorn samplers (i.e., horizontal water bottle) were the prevalent equipment (Bhat et al., 1969, Matsumoto, 1975, McKee et al., 1984, and Minagawa and Tsunogai, 1980, among others), although a few studies used pumping systems (Lee et al., 1991; Tsunogai et al., 1986) and bottles (Bacon and Rutgers van der Loeff, 1989). In the majority of studies measuring dissolved and particulate 234Th phases, the total 234Th concentration was estimated as the sum of them (see, e.g., Coale and Bruland, 1985, and Murray et al., 1989). Regarding particulate 234Th analyses, most of the studies used filtration systems on volumes between 30 and 700 L, a few studies used bottles (with the Go-Flo model more typical than the Niskin one), and one study introduced the use of pumps (Bacon and Rutgers van der Loeff, 1989) Note that the distinction between the dissolved and particulate phases is generally operational, with the term “dissolved” usually comprising all the phases passing through a pore size cutoff of 0.45 µm (i.e., Bacon and Rutgers van der Loeff, 1989; Dominik et al., 1989; Rutgers van der Loeff and Berger, 1991; Santschi et al., 1979; Schmidt et al., 1990; Wei and Murray, 1991).
A total of 25 published works in refereed journals comprise the 234Th studies of this era, compiled in a total of 24 datasets. Sampling was characterized by cruises mostly in the Pacific Ocean (see Figs. 2a and 4a), with a reduced number of locations sampled (maximum of 29 locations and averaged value of 6 locations per cruise) and a reduced number of data points per study (rarely over 100, averaged value of 60 samples per cruise). A total of 36 cruises were compiled from this era, with a total of 1493 234Th data points. Most surveys took place solely in the NH (29) between April and September (Fig. 5a). Only one expedition surveyed the SH, but a total of six cruises crossed the Equator and sampled in both hemispheres.
Only two studies reported samplings that were part of a selected ocean program, which included the GEOSECS program (Krishnaswami et al., 1976) and the DYFAMED program (Schmidt et al., 1990) (see Table 2 for a summary). Another study took place within the framework of the Joint Chinese–American Field Program (JCAFP) (McKee et al., 1984). A total of nine studies reported sampling TSSs (see, e.g., Tanaka et al., 1983).
During this era, 234Th studies were commonly focused on analyzing the parameters influencing the partitioning of a species between dissolved and particulate phases as a way to understand the mechanisms and rates for the scavenging of particle-reactive species. One way to quantify the scavenging of particle-reactive species is the use of distribution coefficients (Kd) which measure the partitioning of a species between dissolved and particulate phases (McKee et al., 1986). As the knowledge of scavenging increased, novel applications of 234Th were developed, reducing the interest in the dissolved phase of 234Th over time and driving changes in the 234Th data type collected during field expeditions (see next sections).
The majority of the studies reported 238U concentrations along with at least one 234Th phase concentration (684 238U data points reported in this era), but none of them measured POC:234Th (Fig. 6a) as the importance of this parameter was not evinced until era 2 (see Sect. 4.2). 238U was either measured (a total of 6) or derived from salinity (a total of 10) mostly using the relationship from Ku et al. (1977). It is also worth mentioning that very few studies reported simultaneous sampling of complementary non-thorium measurements, such as sediment traps (a total of six studies; see, e.g., Coale and Bruland, 1987, and Tsunogai et al., 1986) or 210Pb–210Po disequilibrium (five studies; see Krishnaswami et al., 1976; Moran and Moore, 1989; Santschi et al., 1979, 1980; Tanaka et al., 1983). None of the studies reported CHN (i.e., POC and/or PON) data.
Finally, in terms of modeling 234Th data, more than half of the studies (56 %, a total of 14) did it, and most of the cases used a two-box model, following Coale and Bruland (1985). Except for Tanaka et al. (1983) who applied both an SS and NSS model to estimate the residence time of 234Th by accounting for the change in the inventory of 234Th with time, all the studies that provided information in this regard assumed SS conditions during sampling, which is not surprising since stations were not usually reoccupied during cruises for the collection of time-series data. The physical advection and diffusion (often referred to as V term) were neglected in most of the cases.
4.2 Era 2: “The Sea Around Us”
1992–2000: Introduction of the empirical determination of POC export from 234Th profiles.
“When I think of the floor of the deep sea… I see always the steady, unremitting, downward drift of materials from above, flake upon flake, layer upon layer… the most stupendous “snowfall” the earth has ever seen.”
– Rachel Carson, The Sea Around Us.
The beginning of era 2 is marked by a new approach that was introduced to estimate POC fluxes from 234Th distributions from samples collected during the U.S. JGOFS North Atlantic Bloom Experiment (NABE) carried out in 1989. During this field experiment, the seminal work of Buesseler et al. (1992) found a clear relationship between the onset of the spring bloom, the subsequent drawdown of nutrients and CO2, the net removal of 234Th, and the flux of POC. Because of the conservative nature of 238U in the ocean, any measurable deficit of 234Th relative to its parent can be assumed to imply a significant removal by scavenging and particle sinking flux over a period of days to weeks before sampling as the mean residence time of 234Th is dictated by its decay constant and removal rate by particles (Coale and Bruland, 1985). Buesseler et al. (1992) postulated the empirical determination of POC export fluxes (in ) from 234Th–238U oceanic disequilibrium following
where POC:234Th is the ratio of POC to 234Th measured on sinking particles at the desired depth z (in µmol dpm−1), and 234Thflux is the 234Th downward flux measured at the same depth (in dpm m−2 d−1).
Equation (1) is the base of the so-called 234Th method, and the POC flux obtained is referred to as 234Th-derived POC flux. Note that the concept for this empirical method was introduced in a conference abstract in one much earlier study in the North Pacific (Tsunogai et al., 1976). Buesseler et al. (1992) proposed that the sinking flux of any element – such as carbon, phosphorus, or nitrogen – could be derived from 234Th flux if the ratio of this element to 234Th on sinking particles is known. Element : 234Th ratios are directly determined from their in situ measurement and vary with both depth and particle size (Buesseler et al., 2006).
The 234Th flux can be calculated by evaluating the change in the corresponding total 234Th concentration with time and the contributions due to horizontal and vertical advection and diffusion processes. The simplest solution to estimate 234Th flux is SS conditions and ignoring advective and diffusive transport. These assumptions are the most commonly used (e.g., Le Moigne et al., 2013a, and references therein) as generally only a single 234Th profile can be measured. The neglection of the physical term became inadequate with the expansion of 234Th research to coastal and more dynamic regimes (Savoye et al., 2006). In the open ocean, the most relevant physical process is vertical upwelling, although there are also areas with downwelling, and it will typically result in underestimations of 234Th export if it is not included (Buesseler et al., 1995). Furthermore, Dunne and Murray (1999) developed a model to estimate advection and diffusion, concluding that incorporating advection to estimate carbon export might overestimate the sinking flux if diffusion is not considered. For the temporal variation in 234Th concentration, alternatively to the SS, an NSS model can be applied when temporal fluctuations in 234Th concentration can be assessed owing to repeated sampling, ideally over the course of 2 to 4 weeks (Resplandy et al., 2012) and only if the same water mass is sampled (Savoye et al., 2006) (i.e., the NSS approach is difficult to assess in dynamical settings).
The study by Buesseler and co-authors motivated an increase in oceanic 234Th measurements in the 1990s, and we consider it one of the main milestones of this era along with the following ones:
1992: introduction of the empirical method for the POC flux estimate from 234Th concentrations proposed by Buesseler et al. (1992);
1992–1993: studies on the role of colloidal material (i.e., colloids <1 µm; Stumm, 1977) in 234Th scavenging (Baskaran et al., 1992; Moran and Buesseler, 1993);
introduction of the use of the 210Pb–210Po pair in a similar manner to the 238U–234Th pair by Shimmield et al. (1995);
development of a regional 3-D 234Th flux model to estimate the physical components of the flux (i.e., the V term) by Buesseler et al. (1995);
1996: beginning of the expansion of the 234Th approach to particulate inorganic carbon fluxes (Bacon et al., 1996);
1998: one TSS project established in the frame of JGOFS program, operated by Taiwan: SEATS: South East Asia Time-series Study station (18∘ N, 116∘ E);
1999: introduction of the 20 L MnO2 co-precipitation technique for 234Th by Rutgers van der Loeff and Moore (1999) to allow particulate and dissolved concentrations to be analyzed from a single aliquot and to be measured by beta counting on board.
In the earlier experiments of this era, bottle POC data were generally compared to 234Th-derived from individual cartridge filters or other particle collectors, such as in Buesseler et al. (1992). Several options of large-volume in situ pumps that allowed for the measurement of POC and 234Th on the same filter emerged during this era: (i) large volume filtration using Challenger Oceanic's submersible pumps, which was introduced by Shimmield et al. (1995), (ii) MULVFS (multiple-unit large-volume filtration system) in situ pumping system by Charette et al. (1999), with large volumes (2500–3500 L) passing sequentially through a 1 µm cartridge pre-filter, and (iii) large volume (400 L) samples collected using in situ battery-operated pump deployed on the CTD rosette frame (Charette and Buesseler, 2000). Ratios were normally determined using small-pore-sized filters, either > 0.4–0.5 µm (Huh and Prahl, 1995; Cochran et al., 1995; Laodong et al., 1997; Santschi et al., 1999) or >1 µm (e.g., Benitez-Nelson et al., 2000; Gustafsson et al., 1997a; Rutgers van der Loeff et al., 1997), typically made of glass or quartz fiber. A total of 10 studies sampled two size fractions determined by filtering through 53 µm (Bacon et al., 1996; Buesseler et al., 1998, 1995; Charette and Moran, 1999; Moran et al., 1997; Moran and Buesseler, 1992; Moran and Smith, 2000; Murray et al., 1996) or 70 µm Nitex screens (Charette and Buesseler, 2000; Cochran et al., 2000), but only one of them reported POC:234Th on both small and large particles. In total, only three studies reported POC:234Th ratios measured with filtration methods (Buesseler et al., 1992; Charette et al., 1999; Murray et al., 1996). Additionally, POC:234Th ratios in sinking particles were collected in sediment traps by a total of six studies, including modern designs such as NBSTs (see, e.g., Buesseler et al., 2000) and surface-tethered particle interceptor traps (PITs) (see, e.g., Buesseler et al., 1994).
A total 43 data sets comprise this era, extracted from a total of 48 publications. Sampling was focused on the Atlantic Ocean (see Figs. 2a and 4b). Surveys in the Pacific Ocean were limited, while increased sampling in the Southern Ocean and field expeditions to the Arctic were conducted. Both the number of expeditions and the locations sampled increased. Despite its short duration (less than a decade), a total of 70 cruises were reported within this era, indicative of the dedicated programs and experiments that marked this era, resulting in 8739 and 1133 data points for 234Th and 238U respectively. Similar to the first era, cruises mainly took place exclusively in the NH (52 cruises), although expeditions both solely to the SH and to both hemispheres increased, with a total of 7 and 11 cruises respectively. Samplings mainly took place within the first semester of the year (Fig. 5b).
As previously mentioned, this period of the 234Th history partially overlapped with the golden years of the JGOFS program, and therefore, many of the studies published during era 2 reported 234Th measurements collected during field expeditions that took place in the frame of this international program. A summary of these activities is provided in Table 2. In the case of U.S. JGOFS, this included 234Th measurements at the BATS TSS (see, e.g., Buesseler et al., 1994, 2000) and during several process studies in well-defined areas at strategic oceanic locations: (1) NABE (North Atlantic Bloom Experiment; http://usjgofs.whoi.edu/research/nabe.html, last access: 1 June 2022) that was one of the first major activities of JGOFS with three cruises along longitude 20∘ W in 1989 – it was published 3 years later by Buesseler et al. (1992); (2) EqPac (Equatorial Pacific; http://usjgofs.whoi.edu/research/eqpac.html, last access: 1 June 2022) process study that was conducted along 140∘ W during year 1992 and included a total of four cruises – it was published between 1994 and 1997 by Bacon et al. (1996), Buesseler et al. (1995), Dunne et al. (1997), and Murray et al. (1996) and extended in the next era by Hernes et al. (2001) and Murray et al. (2005); (3) the Southern Ocean expedition during October and November 1992 published by Rutgers van der Loeff et al. (1997) and expanded in era 3 by Friedrich and Rutgers van der Loeff (2002); (4) Arabian Sea (http://usjgofs.whoi.edu/research/arabian.html, last access: 1 June 2022), beginning in October 1994 and ending in January 1996 and reported a few years later by Buesseler et al. (1998); (5) AESOPS (Antarctic Environment and Southern Ocean Process Study; http://usjgofs.whoi.edu/research/aesops.html, last access: 1 June 2022), which carried out field work between August 1996 and April 1998 and was published within this era by Cochran et al. (2000) and extended in the next era by Buesseler et al. (2001a). Additionally, studies also reported data from other JGOFS expeditions from the following: (6) Indian program, which completed three major sampling expeditions for 234Th to the eastern and central Arabian Sea in April–May 1994, February–March 1995, and July–August 1995 – it was reported by Sarin et al. (1996) and extended in PANGAEA in 2013 (https://doi.org/10.1594/PANGAEA.807500, JGOFS-INDIA, 2013); (7) Canadian program in the northeast Pacific Ocean which had two phases from 1992 to 1994 and from 1995 to 1997, although 234Th was only sampled during the second phase – data were published by Charette et al. (1999); and (8) France DYFAMED program, sampled in 1987 but published in this era by Schmidt et al. (1992) and extended in the next era (see Schmidt et al., 2002a, b). Finally, field work also included (9) the Southern Ocean Iron RElease Experiment (SOIREE; https://www.bco-dmo.org/project/2051, last access: 1 June 2022), which was the first in situ iron fertilization experiment performed in the polar waters of the Southern Ocean. It took place in February 1999 south of the Polar front in the Australian–Pacific sector of the Southern Ocean and was reported in Charette and Buesseler (2000). Data from this iron enrichment experiment were compiled along with others in a common open-access database during the iron SYNTHESIS program (FeSynth; https://www.bco-dmo.org/program/2017, last access: 1 June 2022) started in 2007.
In addition to JGOFS, cruises from another major initiative that included 234Th sampling were with the Ocean Margins Program (OMEX; http://po.msrc.sunysb.edu/omp/, last access: 1 June 2022), a large field-based study with extensive physical, chemical, biological, and geological measurements, carried out on a northwest European shelf break that ran in two phases from 1993 to 1996 and from 1997 to 2000. 234Th data were made available by Hall et al. (2000).
The number of data points measured per cruise significantly increased within this era, with an average of 125 234Th data points reported per cruise in comparison to the 41 data points averaged in era 1. Such an increase was significantly marked for the dissolved and particulate phases, whose measurements increased more than 5-fold relative to those from era 1 (see Fig. 6b). Additionally, measurements to determine POC and PON to 234Th ratios became routine, therefore allowing the estimate of POC fluxes (see Fig. 4b). However, only half of the studies reported 238U concentrations along with 234Th data, in their majority using a variety of 238U–salinity relationships, with Chen et al. (1986) being the prevalent one. An overall 69 % of the studies (33 out of 48 that comprise this era) modeled 234Th data. Time-series data were collected more often than during the first era, likely with the purpose of following the NSS approach (Buesseler et al., 1992, 1995). Nonetheless, the majority of the studies (70 %) that modeled 234Th data assumed SS conditions (see, e.g., Bacon and Rutgers van der Loeff, 1989; Baskaran et al., 1992, and Gustafsson et al., 1997b). A total of 10 studies applied the NSS model, with seven of them combining it with the SS model (see, e.g., Buesseler et al., 1994, Cochran et al., 2000, and Kersten et al., 1998, for the combined use of both approaches). In terms of additional data, 1 study introduced 234Th underway sampling (Hall et al., 2000), a total of 11 studies reported sampling with sediment traps (see, e.g., Cochran et al., 2000, Murray et al., 1996, and Smoak et al., 1999), 10 studies sampled for 210Pb–210Po disequilibrium (e.g., Moran and Moore, 1989; Santschi et al., 1999; Wei and Murray, 1992), and 13 studies reported CHN data (see, e.g., Niven et al., 1995, Rutgers van der Loeff et al., 1997, and Santschi et al., 1999).
4.3 Era 3: “In the Heart of the Sea”
2001–2009: improvements of the 234Th technique.
“At sea, things appear different.”
– Nathaniel Philbrick, In the Heart of the Sea.
The final boost to the widespread and increasing use of 234Th as a particle flux tracer was motivated by the works of Buesseler et al. (2001b) and Benitez-Nelson et al. (2001), which dramatically increased the number of 234Th measurements and marked the third era with the introduction of the small-volume (2–4 L) technique. This procedure modified the 20 L method developed by Rutgers van der Loeff and Moore (1999) in era 2 and uses the lowest sample volumes of all known 234Th methods to date. It not only allowed immediate onboard beta counting of 234Th concentration and avoided some tedious folding sessions but also enhanced both spatial and temporal resolution of particle export.
The revolution that this novel technique brought with it was substantial. The small-volume technique is essential to capture the particle dynamics and export flux variations on scales that could be better related to local biogeochemical conditions. The main advantage is the convenience of handling small volumes and more rapid processing times. Multiple sampling casts are often required for a 20 L sample profile, whereas a 4 L technique usually allows simultaneous sampling of 234Th with other parameters on a single cast (e.g., nutrients, phytoplankton biomass). As a result, this method can be easily applied at sea using samples obtained through CTD rosette water samplers that are available on most research vessels. For that reason, we have chosen the introduction of the small-volume technique as a shifting milestone in the 234Th timeline.
Further improvements of this technique within this era were carried out some years later by Pike et al. (2005) and Cai et al. (2006b), which are major milestones of this era and whose timeline summaries are as follows:
2001: introduction of the small-volume technique by Buesseler et al. (2001b) and Benitez-Nelson et al. (2001);
one long-term multidisciplinary and moored observatory established in the northwest Atlantic and coordinated by the National Oceanographic Center of Southampton (UK) at the PAP site: Porcupine Abyssal Plain (49–13.5∘ E);
expansion of the 234Th approach to biogenic silica fluxes (Friedrich and Rutgers van der Loeff, 2002);
2005: introduction of the use of yield tracers – double spike technique – for the sake of maintaining the reproducibility (Pike et al., 2005), the advantage of this modified approach being a precise knowledge of 234Th recovery, leading to an enhancement in data quality of 234Th, which is standardly used nowadays and recommended by the GEOTRACES protocol (Maiti et al., 2012);
2006: reduction of the filtration time and introduction of the alpha spectrometric measurement of 230Th recovery by means of using a combination of water bath heating and a reduction in reagent quantities (Cai et al., 2006b), which also modified the typical ion-exchange chemistry to allow for the alpha spectrometric measurement of 230Th recovery.
Moreover, a technological innovation was introduced during era 3 with the development of two in situ pumping systems for high volume filtration for 234Th concentrations and POC:234Th ratios in sinking particles widely used from this era on (1) McLane large-volume water transfer system (WTS-LV) pumps by McLane Laboratories (Falmouth, MA) and (2) SAPS (stand-alone pump system) by Challenger Oceanic (Surrey, UK). Moreover, one study reported the use of a novel split flow-thin cell fractionation (SPLITT) (see Gustafsson et al., 2006).
This has been the golden age of the 234Th so far in terms of publications released by year (almost 10, versus 1 and 6 in eras 1 and 2), with a total of 159 cruises reported in a period of 9 years. A total of 19 676 and 4567 data points for 234Th and 238U respectively (see Figs. 4c and 6c) were compiled in 76 datasets, extracted from 87 studies (81 publications in refereed journals, 1 PhD thesis, and 5 repositories). Data reported in the context of selected ocean programs continued (see Table 2 for more details). This included JGOFS through the TSSs of HOT (C. Benitez-Nelson et al., 2001), BATS (Sweeney et al., 2003), and DYFAMED (e.g., Szlosek et al., 2009), as well as OMEX (Schmidt et al., 2002b). Other new studies, such as the Carbon Retention In A Colored Ocean (CARIACO; https://www.st.nmfs.noaa.gov/copepod/time-series/ve-10101/, last access: 6 June 2022) time-series program operative between 1995 and 2017 and published by Smoak et al. (2004), were also initiated. Additionally, novel JGOFS initiatives took place: (1) JGOFS-France MEDATLANTE (http://www.obs-vlfr.fr/cd_rom_dmtt/other_main.htm, last access: 6 June 2022) in the Gibraltar Strait and the northeast Atlantic Ocean – data were made available by Schmidt et al. (2009); (2) JGOFS-France ANTArctic RESearch program (ANTARES; http://www.obs-vlfr.fr/cd_rom_dmtt/an_main.htm, last access: 6 June 2022) – data published by Coppola et al. (2005); (3) JGOFS-France DYNAPROC (http://www.obs-vlfr.fr/cd_rom_dmtt/other_main.htm, last access: 6 June 2022) cruise, reported by Schmidt et al. (2002a, 2009); and (4) the JGOFS-Japan North Pacific Process Study carried out at KNOT station (44∘ N, 155∘ E; https://www.nodc.noaa.gov/archive/arc0013/0001873/1.1/data/1-data/general/res_outline/KNOT.html, last access: 6 June 2022) by Kawakami and Honda (2007). Data from a great number of projects and experiments were published during this era (see Table S3 for a chronological summary).
The publications included in this era report data covering the entire ocean and with an increased number of data points in all regions, except the Indian Ocean (see Figs. 2a and 4c). Expeditions to the SH increased, with 18 reported, yet were far below those in the NH, where a total of 134 cruises were undertaken (see Fig. 5c). Additionally, a total of seven surveys sampled in both hemispheres. Stations included the long-term observatories previously sampled for 234Th along with novel ones, such as the PAP site (Turnewitsch and Springer, 2001). Fieldwork took place throughout the entire year, with a remarkable number of cruises in March. Both the overall number of data points and the data points measured per year increased due to the large number of field expeditions reported during this era and the widespread use of the small volume technique. An average of 2183 234Th data points were reported per year in comparison to an average of 60 and 971 data points during eras 1 and 2 respectively. As for the 234Th sample types in this era, the total number of measurements significantly increased for all phases (2-fold for dissolved and particulate and 4-fold for total) and for POC:234Th ratios, and the number remains constant for PON:234Th (see Fig. 6c).
A great increase in the number of data points also was detected for 238U activities, with an increase of 4-fold in the data points. Once again, derived salinity was the most extended approach, with almost all the studies using Chen et al. (1986).
A total of 66 studies out of the 87 that comprise this era (i.e., 76 %) modeled 234Th data: 42 of them applied the SS model (see, e.g., Amiel et al., 2002, Guo et al., 2002, and Speicher et al., 2006), 2 applied the NSS one (Kawakami et al., 2004; Smoak et al., 2004), and 22 studies applied both approaches (e.g., Amiel and Cochran, 2008; Gustafsson et al., 2004; Kim and Church, 2001).
In terms of sampling strategy, 2 studies reported 234Th underway sampling (Rutgers van der Loeff, 2007; Schmidt et al., 2002b), and 30 studies reported the use of sediment traps, with 24 of them measuring POC:234Th ratios (Charette et al., 2001, Schmidt et al., 2002a, and Sweeney et al., 2003, among others). Around a third of the studies reported CHN measurement data (see, e.g., Lepore et al., 2009, and Santschi et al., 2003), while a very reduced number of the studies, around 10 %, analyzed 210Po (see Porcelli et al., 2001, and Somayajulu et al., 2002, among others).
4.4 Era 4: “Twenty Thousand Leagues under the Sea”
2010–present: GEOTRACES program and a new way to study the ocean.
“The sea is everything. It covers seven tenths of the terrestrial globe. Its breath is pure and healthy. It is an immense desert, where man is never lonely, for he feels life stirring on all sides. The sea is only the embodiment of a supernatural and wonderful existence.”
– Jules Verne, Twenty Thousand Leagues under the Sea.
The beginning of this era is identified with the first publication of 234Th data from a GEOTRACES cruise, reported by Cai et al. (2010). GEOTRACES is an international study of the marine biogeochemical cycles of trace elements and their isotopes which changed the way to explore the oceans by combining ocean sections, process studies, data syntheses, and modeling. Its launch marked the beginning of internationally dedicated large-scale collaborative projects characterized by long field surveys with very high spatial resolution and many different parameters measured simultaneously. For this reason, the initial 234Th-related GEOTRACES publication was chosen as the milestone that starts the – so far – final era in the 234Th timeline.
The history of GEOTRACES dates back to 2000, when the initial idea started with group discussions at international meetings inspired by both the successes and the limitations of GEOSECS and JGOFS. After some years in the planning and enabling phase, the GEOTRACES Science Plan was published in 2006. During 2007–2009 the first GEOTRACES cruises took place, including those that were part of the International Polar Year (IPY; https://www.geotraces.org/geotraces-in-the-international-polar-year/, last access: 1 June 2022) devoted to detecting and understanding a suite of trace elements and isotopes in the Arctic and Antarctic marine environments, and the intercalibration cruises (to the Atlantic and Pacific oceans in 2008 and 2009 respectively). A GEOTRACES transect in the Drake Passage was also carried out in 2008 (GIPY05, Germany, ZERO, and DRAKE) in the framework of IPY. Finally, the GEOTRACES program formally launched its seagoing effort in January 2010 and was fully announced to the scientific community at the Ocean Sciences Meeting that year in Portland (Oregon, USA). Numerous cruises have taken place since then, with many of them including 234Th sampling. Many of these results have been reported in the Intermediate Data Products, the first one released in 2014 (IDP2014 by Mawji et al., 2015), the second one in 2017 (IDP2017 by Schlitzer et al., 2018), and the third and most recent one in 2021 (IDP2021 by GEOTRACES Intermediate Data Product Group, 2021).
The GEOTRACES program brought a new philosophy that, in the context of 234Th, drove a shift from mostly deriving POC fluxes only to include trace metal fluxes (see, e.g., Black et al., 2018) and the implementation of standards and intercalibration initiatives to establish procedures and protocols for sampling at sea to ensure that samples are collected, handled, and stored without contamination or other sources of bias (see, e.g., the versions of the Cookbook by GEOTRACES Standards and Intercalibration Committee (Cutter et al., 2014, 2017)). This era includes the development of new technologies to accelerate the collection and analysis of samples, the intercalibration of those technologies to ensure internal consistency among the participating labs, the development of a data management system to facilitate access to the results to the entire oceanographic community, and a broad collaborative effort to model, synthesize, and interpret the results. The most remarkable milestones for this era are as follows:
initial publication of 234Th from a GEOTRACES cruise by Cai et al. (2010), which reported data from ARK XXII/2 expedition to the Arctic Ocean in 2007 carried out in the context of the IPY GEOTRACES program (GIPY11, Germany);
intercalibration initiative by Cutter et al. (2010) to ensure that 234Th results produced by different groups were comparable and internally consistent by using deep waters or stored samples as standards in which 234Th and 238U are known to be in secular equilibrium;
2012: intercalibration initiative by Maiti et al. (2012), which carried out an intercomparison of 234Th measurements in both water and particulate samples between 15 laboratories worldwide;
2014: release of the first GEOTRACES IDP (Intermediate Data Product; Mawji et al., 2015);
2017: release of the second GEOTRACES IDP (Schlitzer et al., 2018);
improvement of the small-volume technique recently carried out by Clevenger et al. (2021), which introduces a revised protocol that decreases sample volumes to 2 L, shortens wait times between steps, and simplifies the chemical recovery process, expanding the ability to more rapidly and safely apply the 234Th method;
release of the third GEOTRACES IDP (GEOTRACES Intermediate Data Product Group, 2021).
A total of 80 data sets were compiled from this era, including 9 previously unpublished ones, extracted from a total of 82 studies (65 publications in refereed journals, 4 PhD theses, and 4 data repositories). A total of 114 cruises and 26 755 and 11 872 data points for 234Th and 238U respectively were compiled, mostly distributed between the Atlantic and Pacific oceans and, to a lesser extent, the Southern Ocean (see Fig. 2a). This era is the second most productive, after era 3, in terms of publications released per year (seven per year). It is also the most intense in terms of sampling, with an average of 235 234Th measurements reported by cruise and over 2400 234Th data points reported by year. Once again, the NH dominated the surveys (79 cruises sampled exclusively above the Equator), particularly numerous in early spring and fall (see Fig. S1). Nonetheless, this era reports the highest number of cruises to the SH, with a total of 27 samplings exclusively below the Equator and an additional 8 cruises sampling in both hemispheres.
More than half of the expeditions of this era reported data from cruises that took place in the framework of major ocean programs (see Table 2) and some minor projects, such as the (i) Arctic Ocean 2001 (AO-01) expedition, reported by Gustafsson and Andersson (2012); (ii) the second and third Chinese National Arctic Research Expedition (CHINARE-2 and CHINARE-3), carried out in 2003 and 2008 respectively and published by Yu et al. (2010, 2012); (iii) Indo–German iron fertilization experiment LOHAFEX (https://epic.awi.de/id/eprint/21440/, last access: 1 June 2022) in 2009, published 4 years later by Martin et al. (2013); (iv) second KErguelen Ocean and Plateau compared Study expedition (KEOPS2) of 2011, published by Planchon et al. (2015); and (v) fate of the northwestern Mediterranean open sea spring bloom (FAMOSO; http://digital.csic.es/handle/10261/94572, last access: 1 June 2022) project, which took place between March and September 2009 and was personally communicated by Viena Puigcorbé to be included in this compilation. Furthermore, 46 % of the data sets included 234Th data from an established time-series location (see Fig. 1c).
An interesting characteristic of this period is that a relatively smaller number of cruises produced a greater amount of data in comparison to previous eras. The most relevant peaks are found in years 2013 and 2015, which coincides with the publication of several GEOTRACES transects (see Sect. 3). Dissolved 234Th measurements reduced drastically (4-fold), while the rest of measurement types increased to some extent, most notably for total 234Th and 238U (see Fig. 6d, note the change in the scale of this plot throughout the eras). Once again, 238U derived from salinity was the most commonly used approach with almost all the studies using the U–salinity relationship of Chen et al. (1986) or Owens et al. (2011).
In terms of modeling 234Th data, a total of 64 out of the 82 studies (78 %) modeled 234Th concentrations and specified whether an SS, an NSS, or both models were used. From them, 50 (78 %) studies applied the SS approach (see, e.g., Alkalay et al., 2020, Cai et al., 2010, and Ceballos-Romero et al., 2016), just 1 (2 %) study applied the NSS one (see Kawakami et al., 2015), and a total of 13 (20 %) studies compared both approaches (see Buesseler et al., 2020a, Kim et al., 2011, and Lemaitre et al., 2018, among others). The number of studies carrying out 234Th underway sampling increased to seven (see, e.g., Black et al., 2018, Estapa et al., 2015, and Martin et al., 2013). More than 32 % of the studies reported POC:234Th ratios collected with sediment traps (Haskell et al., 2013, Kawakami et al., 2010, and Maiti et al., 2016, among others). Around a third of the studies (34 %) reported CHN data (see, e.g., Rosengard et al., 2015), while a very reduced number (∼9 %) analyzed 210Po (such as Alkalay et al., 2020; Ceballos-Romero et al., 2016; or Wei et al., 2011).
4.5 Launching of dedicated large-scale collaborative projects: the beginning of era 5?
“Dawn begins pushing back the covers of night and the sun rolls out of bed.”
– Carl Safina, Song for the Blue Ocean.
Significant milestones within recent years are marked by the launching of an unprecedented number of large-scale collaborative projects including 234Th measurements: e.g., (1) PICCOLO: Processes Influencing Carbon Cycling: Observations of the Lower limb of the Antarctic Overturning (UK, 2016–2020, https://roses.ac.uk/piccolo/, last access: 1 June 2022), a project devoted to quantify the crucial processes that determine carbon cycling in the lower limb of the Southern Ocean overturning circulation through observations and models; (2) COMICS: Controls over Ocean Mesopelagic Interior Carbon (UK, 2017–2021, https://www.comics.ac.uk/, last access: 1 June 2022), a research project that aims to quantify the flow of carbon in the ocean's twilight zone (part of the ocean between 100 and 1000 m below the sea surface) in order to more accurately model global climate change; (3) EXPORTS: EXport Processes in the Ocean from Remote Sensing project (USA, 2017–2022, https://www.us-ocb.org/nasa-exports-phase-i/, last access: 1 June 2022), a large-scale NASA-led field campaign that will provide critical information for quantifying the export and fate of upper-ocean net primary production using satellite observations and state of the art ocean technologies; (4) CUSTARD: Carbon Uptake and Seasonal Traits in Antarctic Remineralisation Depth project (UK, 2018–2022, https://roses.ac.uk/custard/, last access: 1 June 2022), an initiative which will examine how seasonal changes in food availability for phytoplankton influences how long carbon is trapped in the ocean in the Southern Ocean; (5) MOBYDICK: Marine Ecosystem Biodiversity and Dynamics of Carbon around Kerguelen: an integrated view (France, 2017–2022, https://mobydick.mio.osupytheas.fr/, last access: 1 June 2022), a project that combines investigation of the BCP and the end-to-end structure of the pelagic food web; (6) OTZ: Ocean Twilight Zone (USA, 2018–2024, https://twilightzone.whoi.edu/, last access: 1 June 2022), a project devoted to the study of this region of the ocean, with particular emphasis on development of new technologies for scientific exploration of the biomass and biodiversity, animal lives and behavior, food web interactions, and flow of carbon through the twilight zone; and (7) SOLACE: Southern Ocean Large Area Carbon Export (Australia, December 2020–January 2021, https://solace2020.net/, last access: 1 June 2022), a 6-week voyage aimed at developing an approach to quantify the changing effectiveness of CO2 sequestration by the BCP using the remote sensing of the ocean surface by satellites and its interior by autonomous vehicles (specially BIO-ARGO profiling floats) and MOBYDICK project. Additionally, there is another funded future project that includes 234Th in its methodology: the APERO program – Assessing marine biogenic matter Production, Export and Remineralisation: from the surface to the dark Ocean (France, 2022–2026, with a cruise planned for 2023 in the western North Atlantic, https://www.polemermediterranee.com/Activites-Projets/Ressources-biologiques-marines/APERO, last access: 1 June 2022). The Joint Exploration of the Twilight Zone Ocean Network (JETZON; https://www.jetzon.org/, last access: 1 June 2022) is a UN Ocean Decade Program that was created in 2020 to serve as a focal point for twilight zone studies. It includes 234Th measurements as one of the key methodologies and aims at acting as an international coordinating umbrella of projects such as COMICS, EXPORTS, CUSTARD, OTZ, SOLACE, APERO, and PICCOLO, among many others, providing a link between researchers working on these projects through JETZON so that cruises, data, results, and conclusions are shared.
Note that so far, only data from the first expeditions of the EXPORTS project have been published (Buesseler et al., 2020a) and are available in the compilation (see peak in Fig. 2b and d). The benefits to be derived from the success of these endeavors and the inclusion of the remaining data in the compilation could trigger the beginning of a new era for the 234Th technique (i.e., era 5). Whether or not the publication of the 234Th measurements collected during these dedicated large-scale collaborative projects would mark the beginning of era 5 is yet to be known.
We present here two perspectives that will improve the 234Th global data set and broaden its applicability: detect ocean regions with low 234Th measurements and identify which parameters could be useful to include in future versions of the compilation for a wider application of 234Th data.
5.1 Recommendations on 234Th sampling
During the last few decades, considerable progress has been made towards unraveling the behavior of the BCP and understanding the factors influencing the carbon dynamics and the ocean carbon cycle, e.g., primary production, aggregation, ballasting, and the activities of zooplankton and bacteria (see reviews by, e.g., Buesseler and Boyd, 2009, De La Rocha and Passow, 2007, Sanders et al., 2014, and Turner, 2002). Capturing the spatiotemporal variability in 234Th concentrations could play a key role on our precise quantification of carbon uptake, storage rates, and subsequent ecosystem impacts. Strategies up to now have included time series of process studies in key ocean regions, global surveys of carbon parameters, TSSs, and models and databases built from field observations. However, there are gaps in the ship-based 234Th sampling.
In terms of spatial distribution, the SH remains clearly undersampled. Of the total of 5134 locations compiled, 3351 belong to the NH (which accounts for a total of 65 % of the sampling locations) and only 1749 to the SH (35 %), with the 34 remaining ones corresponding to the Equator (<1 %). This is the result of the majority of expeditions taking place in the NH: 78 % solely in the NH and 8 % as part of surveys in both hemispheres.
Figure 1a highlights an especially important gap in the South Pacific region and some additional notable gaps in the data set in the Benguela system (although this was included in the COMICS project, and data will be available in the near future), the Mauritanian upwelling, and the southern Indian Ocean. More attention should be paid to these regions when planning future expeditions for 234Th sampling. Moreover, Fig. 1c shows numerous established time-series stations that have never been sampled for 234Th, and we recommend visiting them in the next expeditions.
In terms of temporal distribution, research cruises are frequently conducted between January and October, although data are skewed to early spring and summer in both hemispheres (see peak in March and October in Fig. S1b). This is especially important for the SH, in the Southern Ocean, where tough wintertime conditions complicate shipboard operations, and research cruises are therefore frequently skewed to calmer spring and summer months. This means that sampling in the Southern Ocean mostly occurs during bloom conditions, which affects the reliability of the SS approach to quantify carbon export from 234Th data (e.g., Buesseler et al., 1995; Ceballos-Romero et al., 2018; Maiti et al., 2008; Resplandy et al., 2012; Savoye et al., 2006). Therefore, results in the Southern Ocean are biased, when compared to the results in other areas, as they correspond mainly to POC fluxes in bloom conditions, whereas in the rest of the oceans, pre- and post-bloom conditions are also included in the global analyses.
Given that the sampling period is not always up to choice, especially when surveying rough seas, in the next section we recommend a series of ancillary parameters to 234Th data, often missed in the interpretation of 234Th results, that will be useful to accurately interpret the results in those specific situations. Furthermore, these complementary parameters will ensure accuracy when (i) interpreting 234Th deficits, (ii) temporally contextualizing 234Th-derived export results, and (iii) extrapolating export results to longer timescales for annual patterns and global estimates of the BCP.
5.2 Recommendations on 234Th ancillary parameters
It is worth mentioning that there is a vast amount of data that can be useful to report in a 234Th compilation due to the wide applicability that has been shown for this technique throughout the years. However, for the sake of feasibility, we had to set boundaries, and we left some parameters out of this first version of the compilation. Nevertheless, we would like to emphasize the dynamic character of this compilation, which has been conceived as an enduring compilation. Thus, the authors will keep the data set “alive” by means of (i) identifying new 234Th data sets to be included, (ii) adding new data provided by direct contact to us by 234Th data measurers, (iii) amending existing data sets if errors are detected or reported, and (iv) extending the amount of parameters included in the data sets.
Following the dynamic spirit behind this effort, we will periodically update the compilation in PANGAEA. As so, we acknowledge ways to improve the compilation in future versions of it. Both new data and ancillary parameters to the 234Th measurements will be included in future versions of the compilation, including new useful parameters arising from novel research and also following suggestions from researchers. We recommend 234Th data users to consider the following parameters as essential complements to 234Th data and therefore report them when publishing 234Th studies.
Necessary complementary data to be included in future version of the compilation for the application of the 234Th method are the many auxiliary sensors included on CTDs to measure parameters such as fluorescence or chlorophyll a and PAR (photosynthetically active radiation). These parameters allow us to track the variable depth of sinking POC production and choose the integration depth to estimate 234Th fluxes by either using the euphotic zone (see, e.g., Giuliani et al., 2007), the PAR depth (e.g., Rosengard et al., 2015), or the primary production zone (e.g., Owens et al., 2015). The integration depth used to estimate POC fluxes has been shown to impact the quantification of the “strength” (i.e., magnitude) of the BCP (Buesseler et al., 2009, 2020b). Therefore, fluorescence and/or PAR data combined with 234Th data are expected to resolve the mechanisms that control the transfer of carbon to the depths by means of the BCP by normalizing POC flux to the depth where it is produced and below which only particle flux attenuation occurs so that progress can be made on untangling the relationships between POC flux and primary production, food web controls, and variable sinking and degradation rates, among others (see Sect. 6 for new studies proposed in this direction). However, most of these auxiliary sensors have only been recently incorporated into the CTD (Jijesh et al., 2017). On the contrary, temperature and salinity data have been a focal point of oceanography since the late 19th century and fully overlap with the 50 years of the 234Th technique. It is for that reason that the temperature and salinity were the only CTD parameters included in this initial version of the compilation. We acknowledge fluorescence and PAR data are crucial parameters for an accurate use of 234Th disequilibrium to evaluate POC export, and they will therefore be added in future versions of the data set. We recommend 234Th data users to consider these data as essential ancillary parameters to 234Th data and therefore report them when publishing 234Th studies.
On the other hand, regarding gaps in parameters overall, only 36 % of the studies compiled provided information regarding bloom conditions and bloom stage during sampling, which prevents us from assessing the reliability of the assumption of SS and NSS conditions to calculate 234Th fluxes. Most of these studies (72 %) followed the SS approach, while 24 % of them combined it with the NSS one, and only 4 % applied solely the NSS model. The reliability of the SS and NSS approaches applied to 234Th deficits to estimate the POC flux depends on the sampling time in relation to the bloom dynamics. The available information on the bloom timing and/or peak flux date and/or duration detailed by station is a key requirement for a quantitative evaluation of the overall accuracy of current 234Th SS-derived POC flux estimates (see, e.g., Ceballos-Romero et al., 2016, 2018). Therefore, we recommend providing as much of this information as possible when reporting future 234Th data. Additionally, for future versions of the compilation, in order to include the bloom stage at the sampling moment following a standardized criterion in the metadata, we carry out a revision of up-to-date literature (Cole et al., 2012; Rumyantseva et al., 2019; Thomalla et al., 2015) to select a quantitative and robust method – easy to apply – of determination. In this way, for further datasets, the bloom stage will be reported when available after previous discussions with authors. A standardized criterion to assign a bloom stage to new datasets in the compilation based on sampling date and ocean region will be established.
The efficiency of the BCP at transporting carbon to the deep ocean and regulating atmospheric CO2 levels is affected even by small perturbations to oceanic ecosystems such as seawater chemistry or nutrient distribution (Kwon et al., 2009). Ongoing changes in temperature, oxygen concentration, and stratification of the water column as a result of anthropogenic warming are predicted to alter export and transfer efficiency by different means. Specifically, a reduction in carbon sequestration, and therefore an increase in oceanic emissions of CO2, is expected (Kwon et al., 2009; Le Quéré et al., 2009). More observational data and mechanistic models to describe the particle flux and its attenuation are required in order to unravel and properly quantify the current role of the BCP and provide a baseline for future estimates of oceanic CO2 uptake.
There are many analyses of BCP processes that 234Th data could be used for. Figure 7a shows a global summary of 234Th:238U ratios at 100±10 m of the water column water in the data set (a total of 17 370 data points). Ratios have been categorized as (i) “deficit” for those values whose 234Th concentrations are lower than 238U ones within 10 % of uncertainty (ratio <0.9), (ii) “equilibrium” for those values that have similar concentrations of 234Th and 238U (0.9< ratio <1.1), and (iii) “excess” for those values in which 234Th concentrations are in excess of 238U ones (i.e., ratios >1.1). This figure can be interpreted as the distribution of probability of 234Th reaching equilibrium (or not) with its parent at 100 m. Most of the data points fall within the equilibrium (53 % of the data points) and deficit (39 %) categories, while “excess” data points accounted only for 8 %. A closer look at the deficit data indicates that most of the samples with ratios <0.9 were very close to the equilibrium value. Therefore, most of the data points compiled reach equilibrium around 100 m depth (see peak with 250 samples with ratios =1). This is important because 100 m is the reference depth that many past studies used to calculate POC fluxes (see Fig. 1 in Le Moigne et al., 2013a). It is important to note that the depth where 234Th equilibrium is reached does not necessarily agree with the euphotic zone. Equilibrium is usually re-established below the euphotic zone, at depths ranging from 50 m (e.g., Thomalla et al., 2006) to 500 m (e.g., Owens et al., 2015), for reason not yet clear (see discussion by Rosengard et al., 2015). Therefore, most recent literature recommends using depths relative to the euphotic zone as a reference depth (Buesseler et al., 2020b). Nonetheless, our data show that, in a first approximation, the choice of using a 100 m fixed depth to integrate 234Th fluxes was accurate in many cases.
Overall, Fig. 7a shows at a glance the number of data points in the compilation that could be used to evaluate processes in the upper ocean such as export flux and export efficiency (e.g., Buesseler et al., 2020b), scavenging rates of trace metals (e.g., Black et al., 2018; Lemaitre et al., 2020), or particle sinking velocities (e.g., Villa-Alfageme et al., 2016, 2021) by using “deficit” ratios, as well as those that could be used to study processes such as particle remineralizations (e.g., Usbeck et al., 2002) by using the “excess” ratios. Recent studies have highlighted the role that disaggregation and fragmentation could play in setting the magnitude of flux attenuation (Baker et al., 2017; Briggs et al., 2020; Cavan et al., 2017) and pointed to it as the most important currently unaccounted for process for improving modern-day export flux simulations (Henson et al., 2021). 234Th excess could be useful to study such mechanisms by detecting low-sinking (i.e., <20 m d−1) POC flux below the mixed layer depth (Baker et al., 2017) by high vertical resolution sampling of 234Th concentrations and POC:234Th ratios. Additionally, these data could be used to investigate alternative export pathways, such as active flux by zooplankton and fish diel vertical migration, which is referred to as “active transport” since some of the POC ingested at the surface is transferred to the depths as part of their daily migrations and residence (Saba et al., 2021; Steinberg and Landry, 2017). Quantification of the impact of this so-called migration pump (Boyd et al., 2019) has been elusive as it is only indirectly estimated or modeled, with active flux ranging widely as a percent of the passive flux, from <4 % (Le Borgne and Rodier, 1997) to equal to or larger than the total passive flux measured by classical methods (Yebra et al., 2018). 234Th excess could shed light on this since a local maximum in export should be detected around the deep scattering layer where migrators reside at depth during the day if migrators accounted for >40 % of the gravitational POC flux (Buesseler and Boyd, 2009).
On another note, data from the compilation could be used to provide revised and more robust global estimates of the ocean's BCP by different means, such as (i) evaluating 234Th-derived POC fluxes regionally, (ii) studying the temporal evolution of the BCP strength through time-series data, (iii) studying carbon export at shallow depths, and (iv) globally analyzing carbon export patterns. As a future study, we propose using the compilation to integrate all data sets to a chosen depth – e.g., to the depth of the 0.1 % light level – following the recommendation by Buesseler et al. (2020b) so that different regions of the upper ocean could be compared across seasons and regions to each other in terms of the BCP strength.
In a second example, 234Th–238U disequilibrium could be combined with 210Po–210Pb and/or sediment trap data to analyze simultaneously key parameters for the functioning of the BCP in different temporal and spatial scales (e.g., Ceballos-Romero et al., 2016; Roca-Martí et al., 2016).
Finally, as an example of potential and powerful uses of this compilation, we show the results of Davidson et al. (2021), in which global 234Th concentrations were estimated out of the regionally varying euphotic zone by using data from these data set. 234Th were regressed to a 2.8∘ grid using a suite of machine learning and minimum variance interpolation algorithms. The gridded data were used to drive a 3-D global model using a set of sparse, implicit, and explicit transport matrices derived from a global, coupled general circulation model (Khatiwala et al., 2005). The model predicts an average global concentration of 234Th of 2.03±0.18 dpm L−1 and the greatest concentrations in ocean gyres (Fig. 7b).
Overall, the compilation presented here provides a valuable resource to better understand and quantify how the contemporary oceanic carbon uptake functions and how it will change in future from the multidisciplinary approach that draws knowledge and methodologies from the fields of physics, mathematics, chemistry, biology, oceanography, and marine sciences that is necessary to generate better mechanistic models of the BCP.
The supplement related to this article is available online at: https://doi.org/10.5194/essd-14-2639-2022-supplement.
ECR compiled and formatted the dataset and prepared and reviewed the manuscript. MVA reviewed and formatted the dataset compilation and managed the inclusion of the compilation in PANGAEA. ECR, MVA, and KOB all contributed to the review of the manuscript.
The contact author has declared that neither they nor their co-authors have any competing interests.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
We thank all the authors that have kindly shared data with us via personal communication, with a special mention to Frederic Le Moigne, John Dunne, Michael Stukel, Patrick Martin, and Peter Santschi. Particular recognition to Michiel Rutgers van der Loeff not only for the great amount of data shared – many of them from many years ago – but for also providing detailed explanations to extract the data of interest to the compilation, which has made this enormous undertaking much easier. Special appreciation to Kenneth Bruland and Kenneth Coale for, in addition to data, sharing beautiful memories of the 234Th world.
We would also like to thank Viena Puigcorbé who helped during the preparation of the database.
We also thank Perrin Davidson, Jennifer Kenyon, Cristina García Prieto, and Carlos Núñez-Nevado for their valuable help with the quality control and the review of the compilation for its final release. Special mention in this regard to Pablo López Puentes for his help in the many hours filling in and reviewing Excel spreadsheets.
This work was partially funded by the V Research Programme from the Universidad de Sevilla (Elena Ceballos-Romero) and EU FEDER-Junta de Andalucía funded project US-1263369 (María Villa-Alfageme). Ken O. Buesseler was supported in part by NSF under GEOTRACES, NASA as part of the EXPORTS program, and WHOI as part of the Ocean Twilight Zone project. María Villa-Alfageme and Ken O. Buesseler are also part of an IAEA Coordinated Research Project “Behaviour and effects of natural and anthropogenic radionuclides in the marine environment and their use as tracers for oceanographic studies”.
This paper was edited by Anton Velo and reviewed by Frederic Le Moigne, Viena Puigcorbé, and one anonymous referee.
Alkalay, R., Zlatkin, O., Katz, T., Herut, B., Halicz, L., Berman-Frank, I., and Weinstein, Y.: Carbon export and drivers in the southeastern Levantine Basin, Deep-Sea Res. Pt. II, 171, 104713, https://doi.org/10.1016/j.dsr2.2019.104713, 2020.
Amiel, D. and Cochran, J. K.: Terrestrial and marine POC fluxes derived from234Th distributions and δ13C measurements on the Mackenzie Shelf, J. Geophys. Res.-Ocean., 113, C03S06, https://doi.org/10.1029/2007JC004260, 2008.
Amiel, D., Cochran, J. K., and Hirschberg, D. J.: 234Th/238U disequilibrium as an indicator of the seasonal export flux of particulate organic carbon in the North Water, Deep-Sea Res. Pt. II, 49, 5191–5209, https://doi.org/10.1016/S0967-0645(02)00185-6, 2002.
Anand, S. S., Rengarajan, R., Sarma, V. V. S. S., Sudheer, A. K., Bhushan, R., and Singh, S. K.: Spatial variability of upper ocean POC export in the Bay of Bengal and the Indian Ocean determined using particle-reactive 234Th, J. Geophys. Res.-Ocean., 122, 3753–3770, https://doi.org/10.1002/2016JC012639, 2017a.
Anand, S. S., Rengarajan, R., Shenoy, D., Gauns, M., and Naqvi, S. W. A.: POC export fluxes in the Arabian Sea and the Bay of Bengal: A simultaneous 234Th/238U and 210Po/210Pb study, Mar. Chem., 19820th January, 70–87, https://doi.org/10.1016/j.marchem.2017.11.005, 2017b.
Anand, S. S., Rengarajan, R., and Sarma, V. V. S. S.: 234Th-Based Carbon Export Flux Along the Indian GEOTRACES GI02 Section in the Arabian Sea and the Indian Ocean, Global Biogeochem. Cycles, 32, 417–436, https://doi.org/10.1002/2017GB005847, 2018.
Andersson, P. S., Wasserburg, G. J., Chen, J. H., Papanastassiou, D. A., and Ingri, J.: 238U–234U and 232Th–230Th in the Baltic Sea and in river water, Earth Planet. Sc. Lett., 130, 217–234, https://doi.org/10.1016/0012-821X(94)00262-W, 1995.
Aono, T., Yamada, M., Kudo, I., Imai, K., Nojiri, Y., and Tsuda, A.: Export fluxes of particulate organic carbon estimated from 234Th/238U disequilibrium during the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study (SEEDS 2001), Prog. Oceanogr., 64, 263–282, https://doi.org/10.1016/j.pocean.2005.02.013, 2005.
Bacon, M. P. and Anderson, R. F.: Distribution of thorium isotopes between dissolved and particulate forms in the deep sea, J. Geophys. Res., 87, 2045, https://doi.org/10.1029/jc087ic03p02045, 1982.
Bacon, M. P. and Rutgers van der Loeff, M. M.: Removal of thorium-234 by scavenging in the bottom nepheloid layer of the ocean, Earth Planet. Sc. Lett., 92, 157–164, https://doi.org/10.1016/0012-821X(89)90043-5, 1989.
Bacon, M. P., Cochran, J. K., Hirschberg, D., Hammar, T. R., and Fleer, A. P.: Export flux of carbon at the equator during the eqpac time-series cruises estimated from 234Th measurements, Deep-Sea Res. Pt. II, 43, 1133–1153, https://doi.org/10.1016/0967-0645(96)00016-1, 1996.
Baker, C. A., Henson, S. A., Cavan, E. L., Giering, S. L. C., Yool, A., Gehlen, M., Belcher, A., Riley, J. S., Smith, H. E. K., and Sanders, R.: Slow-sinking particulate organic carbon in the Atlantic Ocean: Magnitude, flux, and potential controls, Global Biogeochem. Cycles, 31, 1051–1065, https://doi.org/10.1002/2017GB005638, 2017.
Baskaran, M. and Santschi, P. H.: The role of particles and colloids in the transport of radionuclides in coastal environments of Texas, Mar. Chem., 43, 95–114, https://doi.org/10.1016/0304-4203(93)90218-D, 1993.
Baskaran, M., Santschi, P. H., Benoit, G., and Honeyman, B. D.: Scavenging of thorium isotopes by colloids in seawater of the Gulf of Mexico, Geochim. Cosmochim. Ac., 56, 3375–3388, https://doi.org/10.1016/0016-7037(92)90385-V, 1992.
Baskaran, M., Santschi, P. H., Guo, L., Bianchi, T. S., and Lambert, C.: 234Th:238U disequilibria in the Gulf of Mexico: The importance of organic matter and particle concentration, Cont. Shelf Res., 16, 353–380, https://doi.org/10.1016/0278-4343(95)00016-T, 1996.
Baskaran, M., Swarzenski, P. W., and Porcelli, D.: Role of colloidal material in the removal of 234Th in the Canada basin of the Arctic Ocean, Deep-Sea Res. Pt. I, 50, 1353–1373, https://doi.org/10.1016/S0967-0637(03)00140-7, 2003.
Baumann, M. S., Moran, S. B., Lomas, M. W., Kelly, R. P., and Bell, D. W.: Seasonal decoupling of particulate organic carbon export and net primary production in relation to sea-ice at the shelf break of the eastern Bering Sea: Implications for off-shelf carbon export, J. Geophys. Res.-Ocean., 118, 5504–5522, https://doi.org/10.1002/jgrc.20366, 2013.
Benitez-Nelson, C., Buesseler, K. O., Karl, D. M., and Andrews, J.: A time-series study of particulate matter export in the North Pacific Subtropical Gyre based on 234Th: 238U disequilibrium, Deep-Sea Res. Pt. I, 48, 2595–2611, https://doi.org/10.1016/S0967-0637(01)00032-2, 2001.
Benitez-Nelson, C. R. and Moore, W. S.: Future applications of 234Th in aquatic ecosystems, Mar. Chem., 100, 163–165, https://doi.org/10.1016/j.marchem.2005.10.010, 2006.
Benitez-Nelson, C. R., Buesseler, K. O., and Crossin, G.: Upper ocean carbon export, horizontal transport, and vertical eddy diffusitivity in the southwestern Gulf of Maine, Cont. Shelf Res., 20, 707–736, https://doi.org/10.1016/S0278-4343(99)00093-X, 2000.
Benitez-Nelson, C. R., Buesseler, K. O., Rutgers van der Loeff, M., Andrews, J., Ball, L., Crossin, G., and Charette, M. A.: Testing a new small-volume technique for determining 234Th in seawater, J. Radioanal. Nucl. Chem., 248, 795–799, https://doi.org/10.1023/A:1010621618652, 2001.
Bhat, S. G., Krishnaswamy, S., Lal, D., Rama, and Moore, W. S.: 234Th/238U ratios in the ocean, Earth Planet. Sc. Lett., 5, 483–491, https://doi.org/10.1016/s0012-821x(68)80083-4, 1969.
Bishop, J. K. B., Edmond, J. M., Ketten, D. R., Bacon, M. P., and Silker, W. B.: The chemistry, biology, and vertical flux of particulate matter from the upper 400 m of the equatorial Atlantic Ocean, Deep-Sea Res., 24, 511–548, https://doi.org/10.1016/0146-6291(77)90526-4, 1977.
Black, E. E., Buesseler, K. O., Pike, S. M., and Lam, P. J.: 234Th as a tracer of particulate export and remineralization in the southeastern tropical Pacific, Mar. Chem., 201, 35–50, https://doi.org/10.1016/j.marchem.2017.06.009, 2018.
Boyd, P. W., Claustre, H., Levy, M., Siegel, D. A., and Weber, T.: Multi-faceted particle pumps drive carbon sequestration in the ocean, Nature, 568, 327–335, https://doi.org/10.1038/s41586-019-1098-2, 2019.
Brew, H. S., Moran, S. B., Lomas, M. W., and Burd, A. B.: Plankton community composition, organic carbon and thorium-234 particle size distributions, and particle export in the Sargasso sea, J. Mar. Res., 67, 845–868, https://doi.org/10.1357/002224009792006124, 2009.
Briggs, N., Dall'Olmo, G., and Claustre, H.: Major role of particle fragmentation in regulating biological sequestration of CO2 by the oceans, Science, 367, 791–793, https://doi.org/10.1126/science.aay1790, 2020.
Broecker, W. S. and Peng, T. H.: Tracers in the Sea, Eldigio Press, Palisades, New York, 1982.
Bruland, K. W. and Coale, K. H.: Surface Water 234Th/238U Disequilibria: Spatial and Temporal Variations of Scavenging Rates within the Pacific Ocean, in: Dynamic Processes in the Chemistry of the Upper Ocean, pp. 159–172, Springer US, Boston, MA, 1986.
Buesseler, K., Ball, L., Andrews, J., Benitez-Nelson, C., Belastock, R., Chai, F., and Chao, Y.: Upper ocean export of particulate organic carbon in the Arabian Sea derived from thorium-234, Deep-Sea Res. Pt. II, 45, 2461–2487, https://doi.org/10.1016/S0967-0645(98)80022-2, 1998.
Buesseler, K. O. and Boyd, P. W.: Shedding light on processes that control particle export and flux attenuation in the twilight zone of the open ocean, Limnol. Oceanogr., 54, 1210–1232, https://doi.org/10.4319/lo.2009.54.4.1210, 2009.
Buesseler, K. O., Bacon, M. P., Cochran, K. J., and Livingston, H. D.: Carbon and nitrogen export during the JGOFS North Atlantic Bloom experiment estimated from 234Th: 238U disequilibria, Deep-Sea Res. Pt. I, 39, 1115–1137, https://doi.org/10.1016/0198-0149(92)90060-7, 1992.
Buesseler, K. O., Michaels, A. F., Siegel, D. A., and Knap, A. H.: A three dimensional time-dependent approach to calibrating sediment trap fluxes, Global Biogeochem. Cycles, 8, 179–193, https://doi.org/10.1029/94GB00207, 1994.
Buesseler, K. O., Andrews, J. A., Hartman, M. C., Belastock, R., and Chai, F.: Regional estimates of the export flux of particulate organic carbon derived from thorium-234 during the JGOFS EqPac program, Deep-Sea Res. Pt. II, 42, 777–804, https://doi.org/10.1016/0967-0645(95)00043-P, 1995.
Buesseler, K. O., Steinberg, D. K., Michaels, A. F., Johnson, R. J., Andrews, J. E., Valdes, J. R., and Price, J. F.: A comparison of the quantity and composition of material caught in a neutrally buoyant versus surface-tethered sediment trap, Deep-Sea Res. Pt. I, 47, 277–294, https://doi.org/10.1016/S0967-0637(99)00056-4, 2000.
Buesseler, K. O., Ball, L., Andrews, J., Cochran, J. K., Hirschberg, D. J., Bacon, M. P., Fleer, A., and Brzezinski, M.: Upper ocean export of particulate organic carbon and biogenic silica in the Southern Ocean along 170∘ W, Deep-Sea Res. Pt. II, 48, 4275–4297, https://doi.org/10.1016/S0967-0645(01)00089-3, 2001a.
Buesseler, K. O., Benitez-Nelson, C., Rutgers van der Loeff, M., Andrews, J., Ball, L., Crossin, G., and Charette, M. A.: An intercomparison of small- and large-volume techniques for thorium-234 in seawater, Mar. Chem., 74, 15–28, https://doi.org/10.1016/S0304-4203(00)00092-X, 2001b.
Buesseler, K. O., Andrews, J. E., Pike, S. M., Charette, M. A., Goldson, L. E., Brzezinski, M. A., and Lance, V. P.: Particle export during the Southern Ocean Iron Experiment (SOFeX), Limnol. Oceanogr., 50, 311–327, https://doi.org/10.4319/lo.2005.50.1.0311, 2005.
Buesseler, K. O., Benitez-Nelson, C. R., Moran, S. B., Burd, A., Charette, M., Cochran, J. K., Coppola, L., Fisher, N. S., Fowler, S. W., Gardner, W. D., Guo, L. D., Gustafsson, Ö., Lamborg, C., Masque, P., Miquel, J. C., Passow, U., Santschi, P. H., Savoye, N., Stewart, G., and Trull, T.: An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of 234Th as a POC flux proxy, Mar. Chem., 100, 213–233, https://doi.org/10.1016/j.marchem.2005.10.013, 2006.
Buesseler, K. O., Lamborg, C., Cai, P., Escoube, R., Johnson, R., Pike, S., Masque, P., McGillicuddy, D., and Verdeny, E.: Particle fluxes associated with mesoscale eddies in the Sargasso Sea, Deep-Sea Res. Pt. II, 55, 1426–1444, https://doi.org/10.1016/j.dsr2.2008.02.007, 2008.
Buesseler, K. O., Pike, S., Maiti, K., Lamborg, C. H., Siegel, D. A., and Trull, T. W.: Thorium-234 as a tracer of spatial, temporal and vertical variability in particle flux in the North Pacific, Deep-Sea Res. Pt. I, 56, 1143–1167, https://doi.org/10.1016/j.dsr.2009.04.001, 2009.
Buesseler, K. O., McDonnell, A. M. P., Schofield, O. M. E., Steinberg, D. K., and Ducklow, H. W.: High particle export over the continental shelf of the west Antarctic Peninsula, Geophys. Res. Lett., 37, L22606, https://doi.org/10.1029/2010GL045448, 2010.
Buesseler, K. O., Benitez-Nelson, C. R., Roca-Martí, M., Wyatt, A. M., Resplandy, L., Clevenger, S. J., Drysdale, J. A., Estapa, M. L., Pike, S., and Umhau, B. P.: High-resolution spatial and temporal measurements of particulate organic carbon flux using thorium-234 in the northeast Pacific Ocean during the EXport Processes in the Ocean from RemoTe Sensing field campaign, Elem. Sci. Anthr., 8, 030, https://doi.org/10.1525/elementa.030, 2020a.
Buesseler, K. O., Boyd, P. W., Black, E. E., and Siegel, D. A.: Metrics that matter for assessing the ocean biological carbon pump, Proc. Natl. Acad. Sci. USA, 117, 9679–9687, https://doi.org/10.1073/pnas.1918114117, 2020b.
Cai, P., Huang, Y., Chen, M., Liu, G., and Qiu, Y.: Export of particulate organic carbon estimated from 234Th-238U disequilibria and its temporal variation in the South China Sea, Chinese Sci. Bull., 46, 1722–1726, https://doi.org/10.1007/bf02900660, 2001.
Cai, P., Huang, Y., Chen, M., Guo, L., Liu, G., and Qiu, Y.: New production based on 228Ra-derived nutrient budgets and thorium-estimated POC export at the intercalibration station in the South China Sea, Deep-Sea Res. Pt. I, 49, 53–66, https://doi.org/10.1016/S0967-0637(01)00040-1, 2002.
Cai, P., Dai, M., Chen, W., Tang, T., and Zhou, K.: On the importance of the decay of 234Th in determining size-fractionated C/234Th ratio on marine particles, Geophys. Res. Lett., 33, L23602, https://doi.org/10.1029/2006GL027792, 2006a.
Cai, P., Dai, M., Lv, D., and Chen, W.: An improvement in the small-volume technique for determining thorium-234 in seawater, Mar. Chem., 100, 282–288, https://doi.org/10.1016/j.marchem.2005.10.016, 2006b.
Cai, P., Dai, M., Lv, D., and Chen, W.: How accurate are 234Th measurements in seawater based on the MnO2-impregnated cartridge technique?, Geochemistry, Geophys. Geosyst., 7, Q03020, https://doi.org/10.1029/2005GC001104, 2006c.
Cai, P., Chen, W., Dai, M., Wan, Z., Wang, D., Li, Q., Tang, T., and Lv, D.: A high-resolution study of particle export in the southern South China sea based on 234Th:238U disequilibrium, J. Geophys. Res.-Ocean., 113, C04019, https://doi.org/10.1029/2007JC004268, 2008.
Cai, P., Rutgers van der Loeff, M., Stimac, I., Nöthig, E. M., Lepore, K., and Moran, S. B.: Low export flux of particulate organic carbon in the central Arctic Ocean as revealed by 234Th:238U disequilibrium, J. Geophys. Res.-Ocean., 115, C10037, https://doi.org/10.1029/2009JC005595, 2010.
Cai, P., Zhao, D., Wang, L., Huang, B., and Dai, M.: Role of particle stock and phytoplankton community structure in regulating particulate organic carbon export in a large marginal sea, J. Geophys. Res.-Ocean., 120, 2063–2095, https://doi.org/10.1002/2014JC010432, 2015.
Cavan, E. L., Trimmer, M., Shelley, F., and Sanders, R.: Remineralization of particulate organic carbon in an ocean oxygen minimum zone, Nat. Commun., 8, 14847, https://doi.org/10.1038/ncomms14847, 2017.
Ceballos-Romero, E., Le Moigne, F. A. C., Henson, S., Marsay, C. M., Sanders, R. J., García-Tenorio, R., and Villa-Alfageme, M.: Influence of bloom dynamics on Particle Export Efficiency in the North Atlantic: a comparative study of radioanalytical techniques and sediment traps, Mar. Chem., 186, 198–210, https://doi.org/10.1016/j.marchem.2016.10.001, 2016.
Ceballos-Romero, E., De Soto, F., Le Moigne, F. A. C., García-Tenorio, R., and Villa-Alfageme, M.: 234 Th-Derived Particle Fluxes and Seasonal Variability: When Is the SS Assumption Reliable? Insights From a Novel Approach for Carbon Flux Simulation, Geophys. Res. Lett., 45, 13414–13426, https://doi.org/10.1029/2018GL079968, 2018.
Ceballos-Romero, E., Buesseler, K. O., Muñoz-Nevado, C., and Villa-Alfageme, M.: More than 50 years of Th-234 data: a comprehensive global oceanic compilation, PANGAEA, https://doi.org/10.1594/PANGAEA.918125, 2021.
Charette, M. A.: Thorium isotope data summaries from R/V Yuzhmorgeologiya, RVIB Nathaniel B. Palmer AMLR2006-Leg1, NBP0606 in the Southern Ocean from January to August 2006 (Ant2006 project, BWZ project), Bco-Dmo, https://www.bco-dmo.org/dataset/3086/data (last access: 1 June 2022), 2009.
Charette, M. A. and Buesseler, K. O.: Does iron fertilization lead to rapid carbon export in the Southern Ocean?, Geochem. Geophys. Geosyst., 1, 2000GC000069, https://doi.org/10.1029/2000GC000069, 2000.
Charette, M. A. and Moran, S. B.: Rates of particle scavenging and particulate organic carbon export estimated using 234Th as a tracer in the subtropical and equatorial Atlantic Ocean, Deep-Sea Res. Pt. II, 46, 885–906, https://doi.org/10.1016/S0967-0645(99)00006-5, 1999.
Charette, M. A., Bradley Moran, S., and Bishop, J. K. B.: 234Th as a tracer of particulate organic carbon export in the subarctic northeast Pacific Ocean, Deep-Sea Res. Pt. II, 46, 2833–2861, https://doi.org/10.1016/S0967-0645(99)00085-5, 1999.
Charette, M. A., Moran, S. B., Pike, S. M., and Smith, J. N.: Investigating the carbon cycle in the Gulf of Maine using the natural tracer thorium 234, J. Geophys. Res.-Ocean., 106, 11553–11579, https://doi.org/10.1029/1999jc000277, 2001.
Chen, J. H., Lawrence Edwards, R., and Wasserburg, G. J.: 238U, 234U and 232Th in seawater, Earth Planet. Sc. Lett., 80, 241–251, https://doi.org/10.1016/0012-821X(86)90108-1, 1986.
Chen, M., Huang, Y., Cai, P., and Guo, L.: Particulate organic carbon export fluxes in the Canada Basin and Bering Sea as derived from 234Th/238U disequilibria, Arctic, 56, 32–44, https://doi.org/10.14430/arctic600, 2003.
Chen, W., Cai, P., Dai, M., and Wei, J.: 234Th/238U disequilibrium and particulate organic carbon export in the northern South China Sea, J. Oceanogr., 64, 417–428, https://doi.org/10.1007/s10872-008-0035-z, 2008.
Clegg, S. L. and Whitfield, M.: A generalized model for the scavenging of trace metals in the open ocean-I. Particle cycling, Deep-Sea Res. Pt. I, 37, 809–832, https://doi.org/10.1016/0198-0149(90)90008-J, 1990.
Clevenger, S. J., Benitez-Nelson, C. R., Drysdale, J., Pike, S., Puigcorbé, V., and Buesseler, K. O.: Review of the analysis of 234Th in small volume (2–4 L) seawater samples: improvements and recommendations, J. Radioanal. Nucl. Chem., 329, 1–13, https://doi.org/10.1007/s10967-021-07772-2, 2021.
Coale, K. H. and Bruland, K. W.: 234Th:238U disequilibria within the California Current, Limnol. Oceanogr., 30, 22–33, https://doi.org/10.4319/lo.1985.30.1.0022, 1985.
Coale, K. H. and Bruland, K. W.: Oceanic stratified euphotic zone as elucidated by 234Th: 238U disequilibria, Limnol. Oceanogr., 32, 189–200, https://doi.org/10.4319/lo.1987.32.1.0189, 1987.
Cochran, J. K. and Masqué, P.: Short-lived U/Th series radionuclides in the ocean: Tracers for scavenging rates, export fluxes and particle dynamics, Rev. Mineral. Geochem., 52, 461–492, https://doi.org/10.2113/0520461, 2003.
Cochran, J. K., Barnes, C., Achman, D., and Hirschberg, D. J.: Thorium-234/uranium-238 disequilibrium as an indicator of scavenging rates and particulate organic carbon fluxes in the Northeast Water Polynya, Greenland, J. Geophys. Res., 100, 4399–4410, https://doi.org/10.1029/94JC01954, 1995.
Cochran, J. K., Buesseler, K. O., Bacon, M. P., Wang, H. W., Hirschberg, D. J., Ball, L., Andrews, J., Crossin, G., and Fleer, A.: Short-lived thorium isotopes (234Th, 228Th) as indicators of poc export and particle cycling in the ross sea, southern ocean, Deep-Sea Res. Pt. II, 47, 3451–3490, https://doi.org/10.1016/S0967-0645(00)00075-8, 2000.
Cochran, J., Buesseler, K. O., Bacon, M. P., and Livingston, H. D.: Thorium isotopes as indicators of particle dynamics in the upper ocean: results from the JGOFS North Atlantic Bloom experiment, Deep-Sea Res. Pt. I, 40, 1569–1595, https://doi.org/10.1016/0967-0637(93)90017-W, 1993.
Cochran, J. K., Miquel, J. C., Armstrong, R., Fowler, S. W., Masqué, P., Gasser, B., Hirschberg, D., Szlosek, J., Rodriguez y Baena, A. M., Verdeny, E., and Stewart, G. M.: Time-series measurements of 234Th in water column and sediment trap samples from the northwestern Mediterranean Sea, Deep-Sea Res. Pt. II, 56, 1487–1501, https://doi.org/10.1016/j.dsr2.2008.12.034, 2009.
Cole, H., Henson, S., Martin, A., and Yool, A.: Mind the gap: The impact of missing data on the calculation of phytoplankton phenology metrics, J. Geophys. Res.-Ocean., 117, C08030, https://doi.org/10.1029/2012JC008249, 2012.
Coppola, L., Roy-Barman, M., Wassmann, P., Mulsow, S., and Jeandel, C.: Calibration of sediment traps and particulate organic carbon export using 234Th in the Barents Sea, Mar. Chem., 80, 11–26, https://doi.org/10.1016/S0304-4203(02)00071-3, 2002.
Coppola, L., Roy-Barman, M., Mulsow, S., Povinec, P., and Jeandel, C.: Low particulate organic carbon export in the frontal zone of the Southern Ocean (Indian sector) revealed by 234Th, Deep-Sea Res. Pt. I, 52, 51–68, https://doi.org/10.1016/j.dsr.2004.07.020, 2005.
Coppola, L., Roy-Barman, M., Mulsow, S., Povinec, P., and Jeandel, C.: Thorium isotopes as tracers of particles dynamics and deep water circulation in the Indian sector of the Southern Ocean (ANTARES IV), Mar. Chem., 100, 299–313, https://doi.org/10.1016/j.marchem.2005.10.019, 2006.
Cutter, G., Andersson, P., Codispoti, L., Croot, P., Francois, R., Lohan, M., and Rutgers van der Loeff, M.: Sampling and sample-handling protocols for GEOTRACES cruises. GEOTRACES cookbook, http://www.geotraces.org/images/stories/documents/intercalibration/Cookbook_v2.pdf (last access: 1 June 2022), 2014.
Cutter, G. A., Andersson, P., Codispoti, L., Croot, P., Place, P., Hoe, T., Kingdom, U., Francois, R., Sciences, O., Lohan, M., Circus, D., and Obata, H.: Sampling and Sample-handling Protocols for GEOTRACES Cruises, GEOTRACES Community Pract., December, 2010.
Cutter, G. A., Casciotti, K., Croot, P. L., Geibert, W., Heimbürger, L.-E., Lohan, M., Planquette, H., and van de Flierdt, T.: Sampling and Sample-handling Protocols for GEOTRACES Cruises. Version 3, August 2017., GEOTRACES Community Pract., August, 139 pp. & Appendices, http://www.geotraces.org/images/stories/documents/intercalibration/Cookbook.pdf (last access: 1 June 2022), 2017.
Dai, M. H. and Benitez-Nelson, C. R.: Colloidal organic carbon and 234Th in the Gulf of Maine, Mar. Chem., 74, 181–196, https://doi.org/10.1016/S0304-4203(01)00012-3, 2001.
Davidson, P., Kenyon, J., Nicholson, D., and Buesseler, K.: An Observationally Constrained, 234Th-Derived Global POC Flux Model, in: An Observationally Constrained, 234Th-Derived Global POC Flux Model, Goldschmidt conference 2021 (virtual), 4–9 July 2021, https://conf.goldschmidt.info/goldschmidt/2021/goldschmidt/2021/meetingapp.cgi/Paper/8027 (last access: 7 June 2021), 2021.
Delanghe, D., Bard, E., and Hamelin, B.: New TIMS constraints on the uranium-238 and uranium-234 in seawaters from the main ocean basins and the Mediterranean Sea, Mar. Chem., 80, 79–93, https://doi.org/10.1016/S0304-4203(02)00100-7, 2002.
De La Rocha, C. L. and Passow, U.: Factors influencing the sinking of POC and the efficiency of the biological carbon pump, Deep-Sea Res. Pt. II, 54, 639–658, https://doi.org/10.1016/j.dsr2.2007.01.004, 2007.
Dominik, J., Schuler, C., and Santschi, P. H.: Residence times of 234Th and 7Be in Lake Geneva, Earth Planet. Sc. Lett., 93, 345–358, https://doi.org/10.1016/0012-821X(89)90034-4, 1989.
Dunne, J. P. and Murray, J. W.: Sensitivity of 234Th export to physical processes in the central equatorial Pacific, Deep-Sea Res. Pt. I, 46, 831–854, https://doi.org/10.1016/S0967-0637(98)00098-3, 1999.
Dunne, J. P., Murray, J. W., Young, J., Balistrieri, L. S., and Bishop, J.: 234Th and particle cycling in the central equatorial Pacific, Deep-Sea Res. Pt. II, 44, 2049–2083, https://doi.org/10.1016/S0967-0645(97)00063-5, 1997.
Eppley, R. W.: New production: history, methods, problems, in: Productivity of the Ocean: Present and Past, edited by: Berger, W. H., Smetacek, V. S., and Wefer, G., Wiley & Sons, New York, 85–97, https://doi.org/10.1126/science.247.4944.865, 1989.
Eppley, R. W. and Peterson, B. J.: Particulate organic matter flux and planktonic new production in the deep ocean, Nature, 282, 677–680, https://doi.org/10.1038/282677a0, 1979.
Estapa, M. L., Siegel, D. A., Buesseler, K. O., Stanley, R. H. R., Lomas, M. W., and Nelson, N. B.: Decoupling of net community and export production on submesoscales in the Sargasso Sea, Global Biogeochem. Cycles, 29, 1266–1282, https://doi.org/10.1002/2014GB004913, 2015.
Evangeliou, N., Florou, H., and Scoullos, M.: POC and particulate 234Th export fluxes estimated using 234Th/238U disequilibrium in an enclosed Eastern Mediterranean region (Saronikos Gulf and Elefsis Bay, Greece) in seasonal scale, Geochim. Cosmochim. Ac., 75, 5367–5388, https://doi.org/10.1016/j.gca.2011.04.005, 2011.
Evangeliou, N., Florou, H., and Psomiadou, C.: Size-fractionated particulate organic carbon (poc) export fluxes estimated using 234Th-238U disequilibria in the saronikos gulf (greece) during winter bloom, Fresenius Environmental Bulletin, 22, 1951–1961, 2013.
Foster, J. M. and Shimmield, G. B.: 234Th as a tracer of particle flux and POC export in the northern North Sea during a coccolithophore bloom, Deep-Sea Res. Pt. II, 49, 2965–2977, https://doi.org/10.1016/S0967-0645(02)00066-8, 2002.
Freeland, H.: A short history of Ocean Station Papa and Line P, Prog. Oceanogr., 75, 120–125, https://doi.org/10.1016/j.pocean.2007.08.005, 2007.
Friedrich, J. and Rutgers van der Loeff, M. M.: A two-tracer (210Po-234Th) approach to distinguish organic carbon and biogenic silica export flux in the Antarctic Circumpolar Current, Deep-Sea Res. Pt. I, 49, 101–120, https://doi.org/10.1016/S0967-0637(01)00045-0, 2002.
Frignani, M., Courp, T., Cochran, J. K., Hirschberg, D., and Vitoria I Codina, L.: Scavenging rates and particle characteristics in and near the Lacaze-Duthiers submarine canyon, northwest Mediterranean, Cont. Shelf Res., 22, 2175–2190, https://doi.org/10.1016/S0278-4343(02)00078-X, 2002.
GEOTRACES Intermediate Data Product Group: The GEOTRACES Intermediate Data Product 2021 (IDP2021), NERC EDS Br. Oceanogr. Data Cent. NOC, https://doi.org/10.5285/cf2d9ba9-d51d-3b7c-e053-8486abc0f5fd, 2021.
Giuliani, S., Radakovitch, O., Frignani, M., and Bellucci, L. G.: Short time scale variations of 234Th/238U disequilibrium related to mesoscale variability on the continental slope of the Gulf of Lions (France), Mar. Chem., 106, 403–418, https://doi.org/10.1016/j.marchem.2007.03.007, 2007.
Gulin, S. B.: Seasonal changes of 234Th scavenging in surface water across the western Black Sea: An implication of the cyclonic circulation patterns, J. Environ. Radioact., 51, 335–347, https://doi.org/10.1016/S0265-931X(00)00079-5, 2000.
Guo, L., Hung, C. C., Santschi, P. H., and Walsh, I. D.: 234Th scavenging and its relationship to acid polysaccharide abundance in the Gulf of Mexico, Mar. Chem., 78, 103–119, https://doi.org/10.1016/S0304-4203(02)00012-9, 2002.
Gustafsson, Ö. and Andersson, P. S.: 234Th-derived surface export fluxes of POC from the Northern Barents Sea and the Eurasian sector of the Central Arctic Ocean, Deep-Sea Res. Pt. I, 68, 1–11, https://doi.org/10.1016/j.dsr.2012.05.014, 2012.
Gustafsson, Ö., Gschwend, P. M., and Buesseler, K. O.: Settling removal rates of PCBs into the northwestern Atlantic derived from 238U-234Th desquilibria, Environ. Sci. Technol., 31, 3544–3550, https://doi.org/10.1021/es970299u, 1997a.
Gustafsson, Ö., Gschwend, P. M., and Buesseler, K. O.: Using 234Th disequilibria to estimate the vertical removal rates of polycyclic aromatic hydrocarbons from the surface ocean, Mar. Chem., 57, 11–23, https://doi.org/10.1016/S0304-4203(97)00011-X, 1997b.
Gustafsson, Ö., Buesseler, K. O., Geyer, W. R., Moran, S. B., and Gschwend, P. M.: An assessment of the relative importance of horizontal and vertical transport of particle-reactive chemicals in the coastal ocean, Cont. Shelf Res., 18, 805–829, https://doi.org/10.1016/S0278-4343(98)00015-6, 1998.
Gustafsson, Ö., Andersson, P., Roos, P., Kukulska, Z., Broman, D., Larsson, U., Hajdu, S., and Ingri, J.: Evaluation of the collection efficiency of upper ocean sub-photic-layer sediment traps: A 24-month in situ calibration in the open Baltic Sea using 234Th, Limnol. Oceanogr. Methods, 2, 62–74, https://doi.org/10.4319/lom.2004.2.62, 2004.
Gustafsson, Ö., Larsson, J., Andersson, P., and Ingri, J.: The POC /234Th ratio of settling particles isolated using split flow-thin cell fractionation (SPLITT), Mar. Chem., 100, 314–322, https://doi.org/10.1016/j.marchem.2005.10.018, 2006.
Hall, I. R., Schmidt, S., McCave, I. N., and Reyss, J. L.: Particulate matter distribution and 234Th/238U disequilibrium along the Northern Iberian Margin: Implications for particulate organic carbon export, Deep-Sea Res. Pt. I, 47, 557–582, https://doi.org/10.1016/S0967-0637(99)00065-5, 2000.
Haskell, W. Z., Berelson, W. M., Hammond, D. E., and Capone, D. G.: Particle sinking dynamics and POC fluxes in the Eastern Tropical South Pacific based on 234Th budgets and sediment trap deployments, Deep-Sea Res. Pt. I, 81, 1–13, https://doi.org/10.1016/j.dsr.2013.07.001, 2013.
Haskell, W. Z., Prokopenko, M. G., Hammond, D. E., Stanley, R. H. R., Berelson, W. M., Baronas, J. J., Fleming, J. C., and Aluwihare, L.: An organic carbon budget for coastal Southern California determined by estimates of vertical nutrient flux, net community production and export, Deep-Sea Res. Pt. I, 116, 49–76, https://doi.org/10.1016/j.dsr.2016.07.003, 2016.
Henson, S., Laufkötter, C., Leung, S., Giering, S., Palevsky, H., and Cavan, E.: Uncertain response of ocean biological carbon export in a changing world, ESSOAR, https://doi.org/10.1002/ESSOAR.10507873.1, 2021.
Hernes, P. J., Peterson, M. L., Murray, J. W., Wakeham, S. G., Lee, C., and Hedges, J. I.: Particulate carbon and nitrogen fluxes and compositions in the central equatorial Pacific, Deep-Sea Res. Pt. I, 48, 1999–2023, https://doi.org/10.1016/S0967-0637(00)00115-1, 2001.
Huh, C.-A. and Beasley, T. M.: Profiles of dissolved and particulate thorium isotopes in the water column of coastal Southern California, Earth Planet. Sc. Lett., 85, 1–10, https://doi.org/10.1016/0012-821X(87)90016-1, 1987.
Huh, C.-A. and Prahl, F. G.: Role of colloids in upper ocean biogeochemistry in the northeast Pacific Ocean elucidated from 238U-234Th disequilibria, Limnol. Oceanogr., 40, 528–532, https://doi.org/10.4319/lo.1995.40.3.0528, 1995.
Hung, C.-C. and Gong, G.-C.: POC/234Th ratios in particles collected in sediment traps in the northern South China Sea, Estuar. Coast. Shelf Sci., 88, 303–310, https://doi.org/10.1016/j.ecss.2010.04.008, 2010.
Hung, C. C. and Gong, G. C.: Export flux of POC in the main stream of the Kuroshio, Geophys. Res. Lett., 34, L18606, https://doi.org/10.1029/2007GL030236, 2007.
Hung, C. C., Guo, L., Roberts, K. A., and Santschi, P. H.: Upper ocean carbon flux determined by the 234Th approach and sediment traps using size-fractionated POC and 234Yj data from the Gulf of Mexico, Geochem. J., 38, 601–611, https://doi.org/10.2343/geochemj.38.601, 2004.
Hung, C. C., Xu, C., Santschi, P. H., Zhang, S. J., Schwehr, K. A., Quigg, A., Guo, L., Gong, G. C., Pinckney, J. L., Long, R. A., and Wei, C. L.: Comparative evaluation of sediment trap and 234Th-derived POC fluxes from the upper oligotrophic waters of the Gulf of Mexico and the subtropical northwestern Pacific Ocean, Mar. Chem., 121, 132–144, https://doi.org/10.1016/j.marchem.2010.03.011, 2010.
Hung, C. C., Gong, G. C., and Santschi, P. H.: 234Th in different size classes of sediment trap collected particles from the Northwestern Pacific Ocean, Geochim. Cosmochim. Ac., 91, 60–74, https://doi.org/10.1016/j.gca.2012.05.017, 2012.
Jacquet, S. H. M., Lam, P. J., Trull, T., and Dehairs, F.: Carbon export production in the subantarctic zone and polar front zone south of Tasmania, Deep-Sea Res. Pt. II, 58, 2277–2292, https://doi.org/10.1016/j.dsr2.2011.05.035, 2011.
JGOFS-INDIA: Thorium 234 measured on water bottle samples during Sagar Kanya cruise SK121, PANGAEA, https://doi.org/10.1594/PANGAEA.807500, 2013.
Jijesh, J. J., Shivashankar, Susmitha, M., Bhanu, M., and Sindhanakeri, P.: Development of a CTD sensor subsystem for oceanographic application, in RTEICT 2017 - 2nd IEEE International Conference on Recent Trends in Electronics, Information and Communication Technology, Proceedings, IEEE, 2018, 1487–1492, 2017.
Kaufman, A., Li, Y. H., and Turekian, K. K.: The removal rates of 234Th and 228Th from waters of the New York Bight, Earth Planet. Sc. Lett., 54, 385–392, https://doi.org/10.1016/0012-821X(81)90054-6, 1981.
Kawakami, H.: Scavenging of 210Po and 234Th by particulate organic carbon in the surface layer of the northwestern North Pacific Ocean, Far East J. Ocean Res., 2, 67–82, 2009.
Kawakami, H.: 234Th and POC dataset in the North Pacific in 2002–2008, Japan Agency Mar. Sci. Technol.. http://www.jamstec.go.jp/res/ress/kawakami/234Th.html (last access: 1 June 2022), 2012.
Kawakami, H. and Honda, M. C.: Time-series observation of POC fluxes estimated from 234Th in the northwestern North Pacific, Deep-Sea Res. Pt. I, 54, 1070–1090, https://doi.org/10.1016/j.dsr.2007.04.005, 2007.
Kawakami, H., Yang, Y. L., Honda, M. C., and Kusakabe, M.: Particulate organic carbon fluxes estimated from 234Th deficiency in winters and springs in the northwestern North Pacific, Geochem. J., 38, 581–592, https://doi.org/10.2343/geochemj.38.581, 2004.
Kawakami, H., Honda, M. C., Matsumoto, K., Fujiki, T., and Watanabe, S.: East-west distribution of POC fluxes estimated from 234Th in the northern North Pacific in autumn, J. Oceanogr., 66, 71–83, https://doi.org/10.1007/s10872-010-0006-z, 2010.
Kawakami, H., Honda, M. C., Matsumoto, K., Wakita, M., Kitamura, M., Fujiki, T., and Watanabe, S.: POC fluxes estimated from 234Th in late spring–early summer in the western subarctic North Pacific, J. Oceanogr., 71, 311–324, https://doi.org/10.1007/s10872-015-0290-8, 2015.
Kershaw, P. and Young, A.: Scavenging of 234Th in the Eastern Irish Sea, J. Environ. Radioact., 6, 1–23, https://doi.org/10.1016/0265-931X(88)90064-1, 1988.
Kersten, M., Thomsen, S., Priebsch, W.. and Garbe-Schönberg, C. D.: Scavenging and particle residence times determined from 234Th/238U disequilibria in the coastal waters of Mecklenburg Bay, Appl. Geochem., 13, 339–347, https://doi.org/10.1016/S0883-2927(97)00103-0, 1998.
Khatiwala, S., Visbeck, M., and Cane, M. A.: Accelerated simulation of passive tracers in ocean circulation models, Ocean Model., 9, 51–69, https://doi.org/10.1016/j.ocemod.2004.04.002, 2005.
Kim, D., Choi, M. S., Oh, H. Y., Song, Y. H., Noh, J. H., and Kim, K. H.: Seasonal export fluxes of particulate organic carbon from 234Th/238U disequilibrium measurements in the Ulleung Basin1 (Tsushima Basin) of the East Sea1 (Sea of Japan), J. Oceanogr., 67, 577–588, https://doi.org/10.1007/s10872-011-0058-8, 2011.
Kim, G. and Church, T. M.: Seasonal biogeochemical fluxes of 234Th and 210Po in the upper Sargasson Sea: Influence from atmosphere iron deposition, Global Biogeochem. Cycles, 15, 651–661, https://doi.org/10.1029/2000GB001313, 2001.
Knauss, K. G., Ku, T. L., and Moore, W. S.: Radium and thorium isotopes in the surface waters of the East Pacific and coastal Southern California, Earth Planet. Sc. Lett., 39, 235–249, https://doi.org/10.1016/0012-821X(78)90199-1, 1978.
Krishnaswami, S., Lal, D., Somayajulu, B. L. K., Weiss, R. F., and Craig, H.: Large-volume in-situ filtration of deep Pacific waters: Mineralogical and radioisotope studies, Earth Planet. Sc. Lett., 32, 420–429, https://doi.org/10.1016/0012-821X(76)90082-0, 1976.
Ku, T. L., Knauss, K. G., and Mathieu, G. G.: Uranium in open ocean: concentration and isotopic composition, Deep-Sea Res., 24, 1005–1017, https://doi.org/10.1016/0146-6291(77)90571-9, 1977.
Kuptsov, V. M., Lisitzin, A. P., and Shevchenko, V. P.: Th-234 as an Indicator of Particulate Fluxes in the Kara Sea, Okeanologiya, 34, 759–765, 1994.
Kwon, E. Y., Primeau, F., and Sarmiento, J. L.: The impact of remineralization depth on the air-sea carbon balance, Nat. Geosci., 2, 630–635, https://doi.org/10.1038/ngeo612, 2009.
Lalande, C., Lepore, K., Cooper, L. W., Grebmeier, J. M., and Moran, S. B.: Export fluxes of particulate organic carbon in the Chukchi Sea: A comparative study using 234Th/238U disequilibria and drifting sediment traps, Mar. Chem., 103, 185–196, https://doi.org/10.1016/j.marchem.2006.07.004, 2007.
Lalande, C., Moran, S. B., Wassmann, P., Grebmeier, J. M., and Cooper, L. W.: 234Th-derived particulate organic carbon fluxes in the northern Barents Sea with comparison to drifting sediment trap fluxes, J. Mar. Syst., 73, 103–113, https://doi.org/10.1016/j.jmarsys.2007.09.004, 2008.
Lamborg, C. H., Buesseler, K. O., Valdes, J., Bertrand, C. H., Bidigare, R., Manganini, S., Pike, S., Steinberg, D., Trull, T., and Wilson, S.: The flux of bio- and lithogenic material associated with sinking particles in the mesopelagic “twilight zone” of the northwest and North Central Pacific Ocean, Deep-Sea Res. Pt. II, 55, 1540–1563, https://doi.org/10.1016/j.dsr2.2008.04.011, 2008.
Lampitt, R. S., Boorman, B., Brown, L., Lucas, M., Salter, I., Sanders, R., Saw, K., Seeyave, S., Thomalla, S. J., and Turnewitsch, R.: Particle export from the euphotic zone: Estimates using a novel drifting sediment trap, 234Th and new production, Deep-Sea Res. Pt. I, 55, 1484–1502, https://doi.org/10.1016/j.dsr.2008.07.002, 2008.
Langone, L., Frignani, M., Cochran, J. K., and Ravaioli, M.: Scavenging processes and export fluxes close to a retreating seasonal ice margin (Ross Sea, Antartica), Water, Air, Soil Pollut., 99, 705–715, https://doi.org/10.1007/bf02406910, 1997.
Laodong, G., Santschi, P. H., and Baskaran, M.: Interactions of thorium isotopes with colloidal organic matter in oceanic environments, Colloids Surfaces A Physicochem. Eng. Asp., 120, 255–271, https://doi.org/10.1016/S0927-7757(96)03723-5, 1997.
Le Borgne, R. and Rodier, M.: Net zooplankton and the biological pump: A comparison between the oligotrophic and mesotrophic equatorial Pacific, Deep-Sea Res. Pt. II, 44, 2003–2023, https://doi.org/10.1016/S0967-0645(97)00034-9, 1997.
Lee, T., Barg, E., and Lal, D.: Studies of vertical mixing in the Southern California Bight with cosmogenic radionuclides 32P and 7Be, Limnol. Oceanogr., 36, 1044–1052, https://doi.org/10.4319/lo.1918.104.22.1684, 1991.
Le Gland, G., Aumont, O., and Mémery, L.: An Estimate of Thorium 234 Partition Coefficients Through Global Inverse Modeling, J. Geophys. Res.-Ocean., 124, 3575–3606, https://doi.org/10.1029/2018JC014668, 2019.
Lemaitre, N.: Multi-proxy approach (234Th, Baxs) of export and remineralisation fluxes of carbon and biogenic elements associated ith the oceanic biological pump, PhD dissertation, Joint PhD with Université de Bretagne Occidentale, Brest, France, Brussels, France, https://we.vub.ac.be/en/phd-nolwenn-lemaitre (last access: 1 June 2022), 2017.
Lemaitre, N., Planquette, H., Dehairs, F., van der Merwe, P., Bowie, A. R., Trull, T. W., Laurenceau-Cornec, E. C., Davies, D., Bollinger, C., Le Goff, M., Grossteffan, E., and Planchon, F.: Impact of the natural Fe-fertilization on the magnitude, stoichiometry and efficiency of particulate biogenic silica, nitrogen and iron export fluxes, Deep-Sea Res. Pt. I, 117, 11–27, https://doi.org/10.1016/j.dsr.2016.09.002, 2016.
Lemaitre, N., Planchon, F., Planquette, H., Dehairs, F., Fonseca-Batista, D., Roukaerts, A., Deman, F., Tang, Y., Mariez, C., and Sarthou, G.: High variability of particulate organic carbon export along the North Atlantic GEOTRACES section GA01 as deduced from 234Th fluxes, Biogeosciences, 15, 6417–6437, https://doi.org/10.5194/bg-15-6417-2018, 2018.
Lemaitre, N., Planquette, H., Dehairs, F., Planchon, F., Sarthou, G., Gallinari, M., Roig, S., Jeandel, C., and Castrillejo, M.: Particulate Trace Element Export in the North Atlantic (GEOTRACES GA01 Transect, GEOVIDE Cruise), ACS Earth Sp. Chem., 4, 2185–2204, https://doi.org/10.1021/acsearthspacechem.0c00045, 2020.
Le Moigne, F. A. C., Henson, S. A., Sanders, R. J., and Madsen, E.: Global database of surface ocean particulate organic carbon export fluxes diagnosed from the 234Th technique, Earth Syst. Sci. Data, 5, 295–304, https://doi.org/10.5194/essd-5-295-2013, 2013a.
Le Moigne, F. A. C., Villa-Alfageme, M., Sanders, R. J., Marsay, C., Henson, S., and García-Tenorio, R.: Export of organic carbon and biominerals derived from 234Th and 210Po at the Porcupine Abyssal Plain, Deep-Sea Res. Pt I, 72, 88–101, https://doi.org/10.1016/j.dsr.2012.10.010, 2013b.
Le Moigne, F. A. C., Pabortsava, K., Marcinko, C. L. J., Martin, P., and Sanders, R. J.: Where is mineral ballast important for surface export of particulate organic carbon in the ocean', Geophys. Res. Lett., 41, 8460–8468, https://doi.org/10.1002/2014GL061678, 2014.
Le Moigne, F. A. C., Poulton, A. J., Henson, S. A., Daniels, C. J., Fragoso, G. M., Mitchell, E., Richier, S., Russell, B. C., Smith, H. E. K., Tarling, G. A., Young, J. R., and Zubkov, M.: Carbon export efficiency and phytoplankton community composition in the Atlantic sector of the Arctic Ocean, J. Geophys. Res.-Ocean., 120, 3896–3912, https://doi.org/10.1002/2015JC010700, 2015.
Le Moigne, F. A. C., Henson, S. A., Cavan, E., Georges, C., Pabortsava, K., Achterberg, E. P., Ceballos-Romero, E., Zubkov, M., and Sanders, R. J.: What causes the inverse relationship between primary production and export efficiency in the Southern Ocean?, Geophys. Res. Lett., 43, 4457–4466, https://doi.org/10.1002/2016GL068480, 2016.
Lepore, K. and Moran, S. B.: Seasonal changes in thorium scavenging and particle aggregation in the western Arctic Ocean, Deep-Sea Res. Pt. I, 54, 919–938, https://doi.org/10.1016/j.dsr.2007.03.001, 2007.
Lepore, K., Moran, S. B., Grebmeier, J. M., Cooper, L. W., Lalande, C., Maslowski, W., Hill, V., Bates, N. R., Hansell, D. A., Mathis, J. T., and Kelly, R. P.: Seasonal and interannual changes in particulate organic carbon export and deposition in the Chukchi Sea, J. Geophys. Res.-Ocean., 112, C10024, https://doi.org/10.1029/2006JC003555, 2007.
Lepore, K., Moran, S. B., Burd, A. B., Jackson, G. A., Smith, J. N., Kelly, R. P., Kaberi, H., Stavrakakis, S., and Assimakopoulou, G.: Sediment trap and in-situ pump size-fractionated POC/234Th ratios in the Mediterranean Sea and Northwest Atlantic: Implications for POC export, Deep Sea Res. Pt. I, 56, 599–613, https://doi.org/10.1016/j.dsr.2008.11.004, 2009.
Le Quéré, C., Raupach, M. R., Canadell, J. G., Marland, G., Bopp, L., Ciais, P., Conway, T. J., Doney, S. C., Feely, R. A., Foster, P., Friedlingstein, P., Gurney, K., Houghton, R. A., House, J. I., Huntingford, C., Levy, P. E., Lomas, M. R., Majkut, J., Metzl, N., Ometto, J. P., Peters, G. P., Prentice, I. C., Randerson, J. T., Running, S. W., Sarmiento, J. L., Schuster, U., Sitch, S., Takahashi, T., Viovy, N., Van Der Werf, G. R., and Woodward, F. I.: Trends in the sources and sinks of carbon dioxide, Nat. Geosci., 2, 831–836, https://doi.org/10.1038/ngeo689, 2009.
Luo, Y.: Applications of U-decay series isotopes to studying the meridional overturning circulation and particle dynamics in the ocean, University of British Columbia, https://doi.org/10.14288/1.0073792, 2013.
Luo, Y., Miller, L. A., De Baere, B., Soon, M., and Francois, R.: POC fluxes measured by sediment traps and 234Th:238U disequilibrium in Saanich Inlet, British Columbia, Mar. Chem., 162, 19–29, https://doi.org/10.1016/j.marchem.2014.03.001, 2014.
Ma, Q., Chen, M., Qiu, Y., and Li, Y.: Regional estimates of POC export flux derived from thorium-234 in the western Arctic Ocean, Acta Oceanol. Sin., 24, 97–108, 2005.
Maiti, K., Benitez-Nelson, C. R., Rii, Y., and Bidigare, R.: The influence of a mature cyclonic eddy on particle export in the lee of Hawaii, Deep-Sea Res. Pt. II, 55, 1445–1460, https://doi.org/10.1016/j.dsr2.2008.02.008, 2008.
Maiti, K., Benitez-Nelson, C. R., and Buesseler, K. O.: Insights into particle formation and remineralization using the short-lived radionuclide, Thoruim-234, Geophys. Res. Lett., 37, L15608, https://doi.org/10.1029/2010GL044063, 2010.
Maiti, K., Buesseler, K. O., Pike, S. M., Benitez-Nelson, C., Cai, P., Chen, W., Cochran, K., Dai, M., Dehairs, F., Gasser, B., Kelly, R. P., Masque, P., Miller, L. A., Miquel, J. C., Moran, B. B., Morris, P. J., Peine, F., Planchon, F., Renfro, A. A., Rutgers van der Loeff, M., Santschi, P. H., Turnewitsch, R., Waples, J. T., and Xu, C.: Intercalibration studies of short-lived thorium-234 in the water column and marine particles, Limnol. Oceanogr. Methods, 10, 631–644, https://doi.org/10.4319/lom.2012.10.631, 2012.
Maiti, K., Bosu, S., D'Sa, E. J., Adhikari, P. L., Sutor, M., and Longnecker, K.: Export fluxes in northern Gulf of Mexico – Comparative evaluation of direct, indirect and satellite-based estimates, Mar. Chem., 184, 60–77, https://doi.org/10.1016/j.marchem.2016.06.001, 2016.
Mann, D. R., Surpreant, L. D., and Casso, S. A.: In situ chemisorption of transuranics from seawater, Nucl. Instruments Methods Phys. Res., 223, 235–238, https://doi.org/10.1016/0167-5087(84)90653-7, 1984.
Martin, P., Lampitt, R. S., Jane Perry, M., Sanders, R., Lee, C., and D'Asaro, E.: Export and mesopelagic particle flux during a North Atlantic spring diatom bloom, Deep-Sea Res. Pt. I, 58, 338–349, https://doi.org/10.1016/j.dsr.2011.01.006, 2011.
Martin, P., Rutgers van der Loeff, M., Cassar, N., Vandromme, P., D'Ovidio, F., Stemmann, L., Rengarajan, R., Soares, M., González, H. E., Ebersbach, F., Lampitt, R. S., Sanders, R., Barnett, B. A., Smetacek, V., and Naqvi, S. W. A.: Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX, Global Biogeochem. Cycles, 27, 871–881, https://doi.org/10.1002/gbc.20077, 2013.
Matsumoto, E.: 234Th238U radioactive disequilibrium in the surface layer of the ocean, Geochim. Cosmochim. Ac., 39, 205–212, https://doi.org/10.1016/0016-7037(75)90172-6, 1975.
Mawji, E., Schlitzer, R., Masferrer, E., Abadie, C., Abouchami, W., Anderson, R. F., Baars, O., Bakker, K., Baskaran, M., Bates, N. R., Bluhm, K., Bowie, A., Bown, J., Boye, M., Boyle, E. A., Branekkec, P., Bruland, K. W., Brzezinski, M. A., Bucciarelli, E., Buesseler, K., Butler, E., Cai, P., Cardinal, D., Casciotti, K., Chaves, J., Cheng, H., Chever, F., Church, T. M., Colman, A. S., Conway, T. M., Croot, P. L., Cutter, G. A., de Baar, H. J. W., de Souza, G. F., Dehairs, F., Deng, F., Thi Dieu, H., Dulaquais, G., Echegoyen-Sanz, Y., Edwards, R. L., Fahrbach, E., Fitzsimmons, J., Fleisher, M., Frank, M., Friedrich, J., Fripiat, F., Galer, S. J. G., Gamo, T., Garcia-Solsona, E., Gerringa, L. J. A., Godoy, J. M., Gonzalez, S., Grossteffan, E., Hatta, M., Hayes, C. T., Heller, M. I., Henderson, G., Huang, K.-F., Jeandel, C., Jenkins, W. J., John, S., Kenna, T. C., Klunder, M., Kretschmer, S., Kumamoto, Y., Laan, P., Labatut, M., Lacan, F., Lam, P. J., Lannuzel, D., Le Moigne, F., Lechtenfeld, O., Lohan, M. C., Lu, Y., Masqué, P., McClain, C. R., Measures, C., Middag, R., Moffett, J., Navidad, A., Nishioka, J., Noble, A., Obata, H., Ohnemus, D. C., Owens, S., Planchon, F., Pradoux, C., Puigcorbé, V., Quay, P., Radic, A., Rehkämper, M., Remenyi, T., Rijkenberg, M. J. A., Rintoul, S., Robinson, L. F., Roeske, T., Rosenberg, M., Rutgers van der Loeff, M., Ryabenko, E., Saito, M. A., Roshan, S., Salt, L., Sarthou, G., Schauer, U., Scott, P., Sedwick, P. N., Sha, L., Shiller, A. M., Sigman, D. M., Smethie, W., Smith, G. J., Sohrin, Y., Speich, S., Stichel, T., Stutsman, J., Swift, J. H., Tagliabue, A., Thomas, A., Tsunogai, U., Twining, B. S., van Aken, H. M., van Heuven, S., van Ooijen, J., van Weerlee, E., Venchiarutti, C., Voelker, A. H. L., Wake, B., Warner, M. J., Woodward, E. M. S., Wu, J., Wyatt, N., Yoshikawa, H., Zheng, X.-Y., Xue, Z., Zieringer, M., and Zimmer, L. A.: The GEOTRACES Intermediate Data Product 2014, Mar. Chem., 177, 1–8, https://doi.org/10.1016/j.marchem.2015.04.005, 2015.
McKee, B. A., DeMaster, D. J., and Nittrouer, C. A.: The use of 234T h238 disequilibrium to examine the fate of particle-reactive species on the Yangtze continental shelf, Earth Planet. Sc. Lett., 68, 431–442, https://doi.org/10.1016/0012-821X(84)90128-6, 1984.
McKee, B. A., DeMaster, D. J., and Nittrouer, C. A.: Temporal variability in the partitioning of thorium between dissolved and particulate phases on the Amazon shelf: implications for the scavenging of particle-reactive species, Cont. Shelf Res., 6, 87–106, https://doi.org/10.1016/0278-4343(86)90055-5, 1986.
Minagawa, M. and Tsunogai, S.: Removal of 234Th from a coastal sea: Funka Bay, Japan, Earth Planet. Sc. Lett., 47, 51–64, https://doi.org/10.1016/0012-821X(80)90103-X, 1980.
Moore, W. S.: Review of the geosecs project, Nucl. Instruments Methods Phys. Res., 223, 459–465, https://doi.org/10.1016/0167-5087(84)90692-6, 1984.
Moran, S. B. and Buesseler, K. O.: Short residence time of colloids in the upper ocean estimated from 238U-234Th disequilibria, Nature, 359, 221–223, https://doi.org/10.1038/359221a0, 1992.
Moran, S. B. and Buesseler, K. O.: Size-fractionated 234Th in continental shelf waters off New England: Implications for the role of colloids in oceanic trace metal scavenging, J. Mar. Res., 51, 893–922, https://doi.org/10.1357/0022240933223936, 1993.
Moran, S. B. and Moore, R. M.: The distribution of colloidal aluminum and organic carbon in coastal and open ocean waters off Nova Scotia, Geochim. Cosmochim. Ac., 53, 2519–2527, https://doi.org/10.1016/0016-7037(89)90125-7, 1989.
Moran, S. B. and Smith, J. N.: 234Th as a tracer of scavenging and particle export in the Beaufort Sea, Cont. Shelf Res., 20, 153–167, https://doi.org/10.1016/S0278-4343(99)00065-5, 2000.
Moran, S. B., Ellis, K. M., and Smith, J. N.: 234Th/238U disequilibrium in the central Arctic Ocean: Implications for particulate organic carbon export, Deep-Sea Res. Pt. II, 44, 1593–1606, https://doi.org/10.1016/S0967-0645(97)00049-0, 1997.
Moran, S. B., Weinstein, S. E., Edmonds, H. N., Smith, J. N., Kelly, R. P., Pilson, M. E. Q., and Harrison, W. G.: Does 234Th/238U disequilibrium provide an accurate record of the export flux of particulate organic carbon from the upper ocean?, Limnol. Oceanogr., 48, 1018–1029, https://doi.org/10.4319/lo.2003.48.3.1018, 2003.
Moran, S. B., Kelly, R. P., Hagstrom, K., Smith, J. N., Grebmeier, J. M., Cooper, L. W., Cota, G. F., Walsh, J. J., Bates, N. R., Hansell, D. A., Maslowski, W., Nelson, R. P., and Mulsow, S.: Seasonal changes in POC export flux in the Chukchi Sea and implications for water column-benthic coupling in Arctic shelves, Deep-Sea Res. Pt. II, 52, 3427–3451, https://doi.org/10.1016/j.dsr2.2005.09.011, 2005.
Moran, S. B., Lomas, M. W., Kelly, R. P., Gradinger, R., Iken, K., and Mathis, J. T.: Seasonal succession of net primary productivity, particulate organic carbon export, and autotrophic community composition in the eastern Bering Sea, Deep-Sea Res. Pt. II, 65–70, 84–97, https://doi.org/10.1016/j.dsr2.2012.02.011, 2012.
Morris, P. J., Sanders, R., Turnewitsch, R., and Thomalla, S.: 234Th-derived particulate organic carbon export from an island-induced phytoplankton bloom in the Southern Ocean, Deep-Sea Res. Pt. II, 54, 2208–2232, https://doi.org/10.1016/j.dsr2.2007.06.002, 2007.
Murray, J. W., Downs, J. N., Strom, S., Wei, C. L., and Jannasch, H. W.: Nutrient assimilation, export production and 234Th scavenging in the eastern equatorial Pacific, Deep-Sea Res. Pt. I, 36, 1471–1489, https://doi.org/10.1016/0198-0149(89)90052-6, 1989.
Murray, J. W., Young, J., Newton, J., Dunne, J., Chapin, T., Paul, B., and McCarthy, J. J.: Export flux of particulate organic carbon from the central equatorial pacific determined using a combined drifting trap- 234Th approach, Deep-Sea Res. Pt. II, 43, 1095–1132, https://doi.org/10.1016/0967-0645(96)00036-7, 1996.
Murray, J. W., Paul, B., Dunne, J. P., and Chapin, T.: 234Th, 210Pb, 210Po and stable Pb in the central equatorial Pacific: Tracers for particle cycling, Deep-Sea Res. Pt. I, 52, 2109–2139, https://doi.org/10.1016/j.dsr.2005.06.016, 2005.
Niskin, S. J.: A water sampler for microbiological studies, Deep. Res. Oceanogr. Abstr., 9, 501–503, https://doi.org/10.1016/0011-7471(62)90101-8, 1962.
Niven, S. E. H., Kepkay, P. E., and Boraie, A.: Colloidal organic carbon and colloidal 234Th dynamics during a coastal phytoplankton bloom, Deep-Sea Res. Pt. II, 42, 257–273, https://doi.org/10.1016/0967-0645(95)00014-H, 1995.
Not, C., Brown, K., Ghaleb, B., and Hillaire-Marcel, C.: Conservative behavior of uranium vs. salinity in Arctic sea ice and brine, Mar. Chem., 130–131, 33–39, https://doi.org/10.1016/j.marchem.2011.12.005, 2012.
Nozaki, Y., Horibe, Y., and Tsubota, H.: The water column distributions of thorium isotopes in the western North Pacific, Earth Planet. Sc. Lett., 54, 203–216, https://doi.org/10.1016/0012-821X(81)90004-2, 1981.
Owens, S. A.: Advances in measurements of particle cycling and fluxes in the ocean, Massachusetts Institute of Technology, http://hdl.handle.net/1721.1/79284, 2013.
Owens, S. A., Buesseler, K. O., and Sims, K. W. W.: Re-evaluating the 238U-salinity relationship in seawater: Implications for the 238U-234Th disequilibrium method, Mar. Chem., 127, 31–39, https://doi.org/10.1016/j.marchem.2011.07.005, 2011.
Owens, S. A., Pike, S., and Buesseler, K. O.: Thorium-234 as a tracer of particle dynamics and upper ocean export in the Atlantic Ocean, Deep-Sea Res. Pt. II, 116, 42–59, https://doi.org/10.1016/j.dsr2.2014.11.010, 2015.
Pabortsava, K.: Downward particle export and sequestration fluxes in the oligotrophic Atlantic Ocean, University of Southampton, https://eprints.soton.ac.uk/372493/ (last access: 1 June 2022), 2014.
Pates, J. M. and Muir, G. K. P.: U-salinity relationships in the Mediterranean: Implications for 234Th:238U particle flux studies, Mar. Chem., 106, 530–545, https://doi.org/10.1016/j.marchem.2007.05.006, 2007.
Pike, S. M., Buesseler, K. O., Andrews, J., and Savoye, N.: Quantification of 234Th recovery in small volume sea water samples by inductively coupled plasma-mass spectrometry, J. Radioanal. Nucl. Chem., 263, 355–360, https://doi.org/10.1007/s10967-005-0062-9, 2005.
Planchon, F., Cavagna, A.-J., Cardinal, D., André, L., and Dehairs, F.: Late summer particulate organic carbon export and twilight zone remineralisation in the Atlantic sector of the Southern Ocean, Biogeosciences, 10, 803–820, https://doi.org/10.5194/bg-10-803-2013, 2013.
Planchon, F., Ballas, D., Cavagna, A.-J., Bowie, A. R., Davies, D., Trull, T., Laurenceau-Cornec, E. C., Van Der Merwe, P., and Dehairs, F.: Carbon export in the naturally iron-fertilized Kerguelen area of the Southern Ocean based on the 234Th approach, Biogeosciences, 12, 3831–3848, https://doi.org/10.5194/bg-12-3831-2015, 2015.
Porcelli, D., Andersson, P. S., Baskaran, M., and Wasserburg, G. J.: Transport of U- And Th-series nuclides in a Baltic Shield watershed and the Baltic Sea, Geochim. Cosmochim. Ac., 65, 2439–2459, https://doi.org/10.1016/S0016-7037(01)00610-X, 2001.
Puigcorbé, V.: Global database of oceanic particulate organic carbon to particulate 234Th ratios, PANGAEA, https://doi.org/10.1594/PANGAEA.911424, 2019.
Puigcorbé, V., Benitez-Nelson, C. R., Masqué, P., Verdeny, E., White, A. E., Popp, B. N., Prahl, F. G., and Lam, P. J.: Small phytoplankton drive high summertime carbon and nutrient export in the Gulf of California and Eastern Tropical North Pacific, Global Biogeochem. Cycles, 29, 1309–1332, https://doi.org/10.1002/2015GB005134, 2015.
Puigcorbé, V., Roca-Martí, M., Masqué, P., Benitez-Nelson, C., Rutgers van der Loeff, M., Bracher, A., and Moreau, S.: Latitudinal distributions of particulate carbon export across the North Western Atlantic Ocean, Deep-Sea Res. Pt. I, 129, 116–130, https://doi.org/10.1016/j.dsr.2017.08.016, 2017a.
Puigcorbé, V., Roca-Martí, M., Masqué, P., Benitez-Nelson, C. R., Rutgers van der Loeff, M., Laglera, L. M., Bracher, A., Cheah, W., Strass, V. H., Hoppema, M., Santos-Echeandía, J., Hunt, B. P. V., Pakhomov, E. A., and Klaas, C.: Particulate organic carbon export across the Antarctic Circumpolar Current at 10∘ E: Differences between north and south of the Antarctic Polar Front, Deep-Sea Res. Pt. II, 138, 86–101, https://doi.org/10.1016/j.dsr2.2016.05.016, 2017b.
Puigcorbé, V., Masqué, P., and Le Moigne, F. A. C.: Global database of ratios of particulate organic carbon to thorium-234 in the ocean: improving estimates of the biological carbon pump, Earth Syst. Sci. Data, 12, 1267–1285, https://doi.org/10.5194/essd-12-1267-2020, 2020.
Radakovitch, O., Frignani, M., Giuliani, S., and Montanari, R.: Temporal variations of dissolved and particulate 234Th at a coastal station of the northern Adriatic Sea, Estuar. Coast. Shelf Sci., 58, 813–824, https://doi.org/10.1016/S0272-7714(03)00187-2, 2003.
Resplandy, L., Martin, A. P., Le Moigne, F., Martin, P., Aquilina, A., Mémery, L., Lévy, M., and Sanders, R.: How does dynamical spatial variability impact 234Th-derived estimates of organic export?, Deep-Sea Res. Pt. I, 68, 24–45, https://doi.org/10.1016/j.dsr.2012.05.015, 2012.
Roca-Martí, M., Puigcorbé, Iversen, V., Hvitfeldt, M., Rutgers van der Loeff, M. M., Klaas, C., Cheah, W., Bracher, A., and Masqué, P.: Thorium-234, POC and PON fluxes during POLARSTERN cruise ANT-XXVIII/3, January–March 2012, Pangaea, https://doi.org/10.1594/PANGAEA.848823, 2015.
Roca-Martí, M., Puigcorbé, V., Rutgers van der Loeff, M. M., Katlein, C., Fernández-Méndez, M., Peeken, I., and Masqué, P.: Carbon export fluxes and export efficiency in the central Arctic during the record sea-ice minimum in 2012: a joint 234Th/238U and study, J. Geophys. Res.-Ocean., 121, 5030–5049, https://doi.org/10.1002/2016JC011816, 2016.
Roca-Martí, M., Puigcorbé, V., Iversen, M. H., Rutgers van der Loeff, M., Klaas, C., Cheah, W., Bracher, A., and Masqué, P.: High particulate organic carbon export during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean, Deep-Sea Res. Pt. II, 138, 102–115, https://doi.org/10.1016/j.dsr2.2015.12.007, 2017.
Rodriguez y Baena, A. M., Metian, M., Teyssié, J. L., De Broyer, C., and Warnau, M.: Experimental evidence for 234Th bioaccumulation in three Antarctic crustaceans: Potential implications for particle flux studies, Mar. Chem., 100, 354–365, https://doi.org/10.1016/j.marchem.2005.10.022, 2006.
Rodriguez y Baena, A. M., Boudjenoun, R., Fowler, S. W., Miquel, J. C., Masqué, P., Sanchez-Cabeza, J. A., and Warnau, M.: 234Th-based carbon export during an ice-edge bloom: Sea-ice algae as a likely bias in data interpretation, Earth Planet. Sc. Lett., 269, 596–604, https://doi.org/10.1016/j.epsl.2008.03.020, 2008.
Rosengard, S. Z., Lam, P. J., Balch, W. M., Auro, M. E., Pike, S., Drapeau, D., and Bowler, B.: Carbon export and transfer to depth across the Southern Ocean Great Calcite Belt, Biogeosciences, 12, 3953–3971, https://doi.org/10.5194/bg-12-3953-2015, 2015.
Rumyantseva, A., Henson, S., Martin, A., Thompson, A. F., Damerell, G. M., Kaiser, J., and Heywood, K. J.: Phytoplankton spring bloom initiation: The impact of atmospheric forcing and light in the temperate North Atlantic Ocean, Prog. Oceanogr., 178, 102202, https://doi.org/10.1016/j.pocean.2019.102202, 2019.
Rutgers van der Loeff, M. and Vöge, I.: Thorium 234/Uranium 238 activity ratios measured on water bottle samples during POLARSTERN cruise ANT-XVIII/2 (EisenEx), PANGAEA, https://doi.org/10.1594/PANGAEA.127229, 2003.
Rutgers van der Loeff, M. M.: Manual determination of Thorium 234 and Uranium 238 during cruise ANT-XXIII/3, PANGAEA, https://doi.org/10.1594/PANGAEA.614765, 2007a.
Rutgers van der Loeff, M. M.: Manual determination of Thorium 234 and Uranium 238 in surface water during cruise ANT-XXIII/3, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, PANGAEA, https://doi.org/10.1594/PANGAEA.615832, 2007b.
Rutgers van der Loeff, M. M. and Berger, G. W.: Scavenging and particle flux: seasonal and regional variations in the Southern Ocean (Atlantic sector), Mar. Chem., 35, 553–567, https://doi.org/10.1016/S0304-4203(09)90042-1, 1991.
Rutgers van der Loeff, M. M. and Moore, W. S.: Determination of natural radioactive tracers, in Methods of Seawater Analysis: Third, Completely Revised and Extended Edition, pp. 365–397, Wiley-VCH Verlag GmbH, Weinheim, Germany, 1999.
Rutgers van der Loeff, M. M., Friedrich, J., and Bathmann, U. V.: Carbon export during the Spring Bloom at the Antarctic Polar Front, determined with the natural tracer 234Th, Deep-Sea Res. Pt. II, 44, 457–478, https://doi.org/10.1016/S0967-0645(96)00067-7, 1997.
Rutgers van der Loeff, M. M., Buesseler, K., Bathmann, U., Hense, I., and Andrews, J.: Comparison of carbon and opal export rates between summer and spring bloom periods in the region of the Antarctic Polar Front, SE Atlantic, Deep-Sea Res. Pt. II, 49, 3849–3869, https://doi.org/10.1016/S0967-0645(02)00114-5, 2002a.
Rutgers van der Loeff, M. M., Meyer, R., Rudels, B., and Rachor, E.: Resuspension and particle transport in the benthic nepheloid layer in and near Fram Strait in relation to faunal abundances and 234Th depletion, Deep-Sea Res. Pt. I, 49, 1941–1958, https://doi.org/10.1016/S0967-0637(02)00113-9, 2002b.
Rutgers van der Loeff, M., Sarin, M. M., Baskaran, M., Benitez-Nelson, C., Buesseler, K. O., Charette, M., Dai, M., Gustafsson, Ö., Masque, P., Morris, P. J., Orlandini, K., Rodriguez y Baena, A., Savoye, N., Schmidt, S., Turnewitsch, R., Vöge, I., and Waples, J. T.: A review of present techniques and methodological advances in analyzing 234Th in aquatic systems, Mar. Chem., 100, 190–212, https://doi.org/10.1016/j.marchem.2005.10.012, 2006.
Rutgers van der Loeff, M. M., Cai, P. H., Stimac, I., Bracher, A., Middag, R., Klunder, M. B., and van Heuven, S. M. A. C.: 234Th in surface waters: Distribution of particle export flux across the Antarctic Circumpolar Current and in the Weddell Sea during the GEOTRACES expedition ZERO and DRAKE, Deep-Sea Res. Pt. II, 58, 2749–2766, https://doi.org/10.1016/j.dsr2.2011.02.004, 2011.
Saba, G. K., Burd, A. B., Dunne, J. P., Hernández-León, S., Martin, A. H., Rose, K. A., Salisbury, J., Steinberg, D. K., Trueman, C. N., Wilson, R. W., and Wilson, S. E.: Toward a better understanding of fish-based contribution to ocean carbon flux, Limnol. Oceanogr., 66, 1639–1664, https://doi.org/10.1002/lno.11709, 2021.
Sanders, R., Morris, P. J., Poulton, A. J., Stinchcombe, M. C., Charalampopoulou, A., Lucas, M. I., and Thomalla, S. J.: Does a ballast effect occur in the surface ocean?, Geophys. Res. Lett., 37, L08602, https://doi.org/10.1029/2010GL042574, 2010.
Sanders, R., Henson, S. A., Koski, M., De La Rocha, C. L., Painter, S. C., Poulton, A. J., Riley, J., Salihoglu, B., Visser, A., Yool, A., Bellerby, R., and Martin, A. P.: The Biological Carbon Pump in the North Atlantic, Prog. Oceanogr., 129, 200–218, https://doi.org/10.1016/j.pocean.2014.05.005, 2014.
Santschi, P. H., Li, Y. H., and Bell, J.: Natural radionuclides in the water of Narragansett Bay, Earth Planet. Sc. Lett., 45, 201–213, https://doi.org/10.1016/0012-821X(79)90121-3, 1979.
Santschi, P. H., Adler, D., Amdurer, M., Li, Y. H., and Bell, J. J.: Thorium isotopes as analogues for “particle-reactive” pollutants in coastal marine environments, Earth Planet. Sc. Lett., 47, 327–335, https://doi.org/10.1016/0012-821X(80)90019-9, 1980.
Santschi, P. H., Guo, L., Baskaran, M., Trumbore, S., Southon, J., Bianchi, T. S., Honeyman, B., and Cifuentes, L.: Isotopic evidence for the contemporary origin of high-molecular weight organic matter in oceanic environments, Geochim. Cosmochim. Ac., 59, 625–631, https://doi.org/10.1016/0016-7037(94)00378-Y, 1995.
Santschi, P. H., Guo, L., Walsh, I. D., Quigley, M. S., and Baskaran, M.: Boundary exchange and scavenging of radionuclides in continental margin waters of the Middle Atlantic Bight: Implications for organic carbon fluxes, Cont. Shelf Res., 19, 609–636, https://doi.org/10.1016/S0278-4343(98)00103-4, 1999.
Santschi, P. H., Hung, C. C., Schultz, G., Alvarado-Quiroz, N., Guo, L., Pinckney, J., and Walsh, I.: Control of acid polysaccharide production and 234Th and POC export fluxes by marine organisms, Geophys. Res. Lett., 30, 2–5, https://doi.org/10.1029/2002GL016046, 2003.
Sarin, M. M., Bhushan, R., Rengarajan, R., and Yadav, D. N.: Simultaneous determination of 238U series nuclides in waters of Arabian Sea and Bay of Bengal, Indian J. Mar. Sci., 21, 121–127, 1992.
Sarin, M. M., Krishnaswami, S., Ramesh, R., and Somayajulu, B. L. K.: 238U decay series nuclides in the northeastern Arabian Sea: Scavenging rates and cycling processes, Cont. Shelf Res., 14, 251–265, https://doi.org/10.1016/0278-4343(94)90015-9, 1994a.
Sarin, M. M., Rengarajan, R., and Somayajulu, B. L. K.: Natural radionuclides in the Arabian Sea and Bay of Bengal: Distribution and evaluation of particle scavenging processes, Proc. Indian Acad. Sci. – Earth Planet. Sci., 103, 211–235, https://doi.org/10.1007/BF02839537, 1994b.
Sarin, M. M., Rengarajan, R., and Ramaswamy, V.: 234Th scavenging and particle export fluxes from the upper 100 m of the Arabian Sea, Curr. Sci., 71, 888–893, 1996.
Savoye, N., Buesseler, K. O., Cardinal, D., and Dehairs, F.: 234Th deficit and excess in the Southern Ocean during spring 2001: Particle export and remineralization, Geophys. Res. Lett., 31, L12301, https://doi.org/10.1029/2004GL019744, 2004.
Savoye, N., Benitez-Nelson, C., Burd, A. B., Cochran, J. K., Charette, M., Buesseler, K. O., Jackson, G. A., Roy-Barman, M., Schmidt, S., and Elskens, M.: 234Th sorption and export models in the water column: A review, Mar. Chem., 100, 234–249, https://doi.org/10.1016/j.marchem.2005.10.014, 2006.
Savoye, N., Trull, T. W., Jacquet, S. H. M., Navez, J., and Dehairs, F.: 234Th-based export fluxes during a natural iron fertilization experiment in the Southern Ocean (KEOPS), Deep-Sea Res. Pt. II, 55, 841–855, https://doi.org/10.1016/j.dsr2.2007.12.036, 2008.
Schlitzer, R., Anderson, R. F., Dodas, E. M., Lohan, M., Geibert, W., Tagliabue, A., Bowie, A., Jeandel, C., Maldonado, M. T., Landing, W. M., Cockwell, D., Abadie, C., Abouchami, W., Achterberg, E. P., Agather, A., Aguliar-Islas, A., van Aken, H. M., Andersen, M., Archer, C., Auro, M., de Baar, H. J., Baars, O., Baker, A. R., Bakker, K., Basak, C., Baskaran, M., Bates, N. R., Bauch, D., van Beek, P., Behrens, M. K., Black, E., Bluhm, K., Bopp, L., Bouman, H., Bowman, K., Bown, J., Boyd, P., Boye, M., Boyle, E. A., Branellec, P., Bridgestock, L., Brissebrat, G., Browning, T., Bruland, K. W., Brumsack, H.-J., Brzezinski, M., Buck, C. S., Buck, K. N., Buesseler, K., Bull, A., Butler, E., Cai, P., Mor, P. C., Cardinal, D., Carlson, C., Carrasco, G., Casacuberta, N., Casciotti, K. L., Castrillejo, M., Chamizo, E., Chance, R., Charette, M. A., Chaves, J. E., Cheng, H., Chever, F., Christl, M., Church, T. M., Closset, I., Colman, A., Conway, T. M., Cossa, D., Croot, P., Cullen, J. T., Cutter, G. A., Daniels, C., Dehairs, F., Deng, F., Dieu, H. T., Duggan, B., Dulaquais, G., Dumousseaud, C., Echegoyen-Sanz, Y., Edwards, R. L., Ellwood, M., Fahrbach, E., Fitzsimmons, J. N., Russell Flegal, A., Fleisher, M. Q., van de Flierdt, T., Frank, M., Friedrich, J., Fripiat, F., Fröllje, H., Galer, S. J. G., Gamo, T., Ganeshram, R. S., Garcia-Orellana, J., Garcia-Solsona, E., Gault-Ringold, M., George, E., Gerringa, L. J. A., Gilbert, M., Godoy, J. M., Goldstein, S. L., Gonzalez, S. R., Grissom, K., Hammerschmidt, C., Hartman, A., Hassler, C. S., Hathorne, E. C., Hatta, M., Hawco, N., Hayes, C. T., Heimbürger, L. E., Helgoe, J., Heller, M., Henderson, G. M., Henderson, P. B., van Heuven, S., Ho, P., Horner, T. J., Hsieh, Y. T., Huang, K. F., Humphreys, M. P., Isshiki, K., Jacquot, J. E., Janssen, D. J., Jenkins, W. J., John, S., Jones, E. M., Jones, J. L., Kadko, D. C., Kayser, R., Kenna, T. C., Khondoker, R., Kim, T., Kipp, L., Klar, J. K., Klunder, M., Kretschmer, S., Kumamoto, Y., Laan, P., Labatut, M., Lacan, F., Lam, P. J., Lambelet, M., Lamborg, C. H., Le Moigne, F. A. C., Le Roy, E., Lechtenfeld, O. J., Lee, J. M., Lherminier, P., Little, S., López-Lora, M., Lu, Y., Masque, P., Mawji, E., Mcclain, C. R., Measures, C., Mehic, S., Barraqueta, J. L. M., van der Merwe, P., Middag, R., Mieruch, S., Milne, A., Minami, T., Moffett, J. W., Moncoiffe, G., Moore, W. S., Morris, P. J., Morton, P. L., Nakaguchi, Y., Nakayama, N., Niedermiller, J., Nishioka, J., Nishiuchi, A., Noble, A., Obata, H., Ober, S., Ohnemus, D. C., van Ooijen, J., O’Sullivan, J., Owens, S., Pahnke, K., Paul, M., Pavia, F., Pena, L. D., Peters, B., Planchon, F., Planquette, H., Pradoux, C., Puigcorbé, V., Quay, P., Queroue, F., Radic, A., Rauschenberg, S., Rehkämper, M., Rember, R., Remenyi, T., Resing, J. A., Rickli, J., Rigaud, S., Rijkenberg, M. J. A., Rintoul, S., Robinson, L. F., Roca-Martí, M., Rodellas, V., Roeske, T., Rolison, J. M., Rosenberg, M., Roshan, S., Rutgers van der Loeff, M. M., Ryabenko, E., Saito, M. A., Salt, L. A., Sanial, V., Sarthou, G., Schallenberg, C., Schauer, U., Scher, H., Schlosser, C., Schnetger, B., Scott, P., Sedwick, P. N., Semiletov, I., Shelley, R., Sherrell, R. M., Shiller, A. M., Sigman, D. M., Singh, S. K., Slagter, H. A., Slater, E., Smethie, W. M., Snaith, H., Sohrin, Y., Sohst, B., Sonke, J. E., Speich, S., Steinfeldt, R., Stewart, G., Stichel, T., Stirling, C. H., Stutsman, J., Swarr, G. J., Swift, J. H., Thomas, A., Thorne, K., Till, C. P., Till, R., Townsend, A. T., Townsend, E., Tuerena, R., Twining, B. S., Vance, D., Velazquez, S., Venchiarutti, C., Villa-Alfageme, M., Vivancos, S. M., Voelker, A. H. L., Wake, B., Warner, M. J., Watson, R., van Weerlee, E., Alexandra Weigand, M., Weinstein, Y., Weiss, D., Wisotzki, A., Woodward, E. M. S., Wu, J., Wu, Y., Wuttig, K., Wyatt, N., Xiang, Y., Xie, R. C., Xue, Z., Yoshikawa, H., Zhang, J., Zhang, P., Zhao, Y., Zheng, L., Zheng, X. Y., Zieringer, M., Zimmer, L. A., Ziveri, P., Zunino, P., and Zurbrick, C.: The GEOTRACES Intermediate Data Product 2017, Chem. Geol., 493, 210–223, https://doi.org/10.1016/j.chemgeo.2018.05.040, 2018.
Schmidt, S.: Impact of the Mediterranean Outflow Water on particle dynamics in intermediate waters of the Northeast Atlantic, as revealed by 234Th and 228Th, Mar. Chem., 100, 289–298, https://doi.org/10.1016/j.marchem.2005.10.017, 2006.
Schmidt, S., Reyss, J. L., Nguyen, H. V., and Buat-Ménard, P.: 234Th cycling in the upper water column of the northwestern Mediterranean Sea, Glob. Planet. Change, 3, 25–33, https://doi.org/10.1016/0921-8181(90)90053-F, 1990.
Schmidt, S., Nival, P., Reyss, J. L., Baker, M., and Buat-Menard, P.: Relation between 234Th scavenging and zooplankton biomass in Mediterranean surface waters, Oceanol. Acta, 15, 227–231, 1992.
Schmidt, S., Andersen, V., Belviso, S., and Marty, J. C.: Strong seasonality in particle dynamics of north-western Mediterranean surface waters as revealed by 234Th/238U, Deep-Sea Res. Pt. I, 49, 1507–1518, https://doi.org/10.1016/S0967-0637(02)00039-0, 2002a.
Schmidt, S., Chou, L., and Hall, I. R.: Particle residence times in surface waters over the north-western Iberian Margin: Comparison of pre-upwelling and winter periods, J. Mar. Syst., 32, 3–11, https://doi.org/10.1016/S0924-7963(02)00027-1, 2002b.
Schmidt, S., Goutx, M., Raimbault, P., Garcia, N., Guibert, P., and Andersen, V.: Th measured particle export from surface waters in north-western Mediterranean: comparison of spring and autumn periods, Biogeosciences Discuss., 6, 143–161, https://doi.org/10.5194/bgd-6-143-2009, 2009.
Schmidt, S., Harlay, J., Borges, A. V., Groom, S., Delille, B., Roevros, N., Christodoulou, S., and Chou, L.: Particle export during a bloom of Emiliania huxleyi in the North-West European continental margin, J. Mar. Syst., 109–110, S182–S190, https://doi.org/10.1016/j.jmarsys.2011.12.005, 2013.
Shaw, T. J., Smith, K. L., Hexel, C. R., Dudgeon, R., Sherman, A. D., Vernet, M., and Kaufmann, R. S.: 234Th-Based Carbon Export around Free-Drifting Icebergs in the Southern Ocean, Deep-Sea Res. Pt. II, 58, 1384–1391, https://doi.org/10.1016/j.dsr2.2010.11.019, 2011.
Shimmield, G. B., Ritchie, G. D., and Fileman, T. W.: The impact of marginal ice zone processes on the distribution of 21OPb, 21OPo and 234Th and implications for new production in the Bellingshausen Sea, Antarctica, Deep-Sea Res. Pt. II, 42, 1313–1335, https://doi.org/10.1016/0967-0645(95)00071-W, 1995.
Smith, K. J., León Vintró, L., Mitchell, P. I., Bally De Bois, P., and Boust, D.: Uranium-thorium disequilibrium in north-east Atlantic waters, J. Environ. Radioactiv., 74, 199–210, 2004.
Smoak, J. M., Moore, W. S., Thunell, R. C., and Shaw, T. J.: Comparison of 234Th, 228Th, and 210Pb fluxes with fluxes of major sediment components in the Guaymas Basin, Gulf of California, Mar. Chem., 65, 177–194, https://doi.org/10.1016/S0304-4203(98)00095-4, 1999.
Smoak, J. M., Benitez-Nelson, C., Moore, W. S., Thunell, R. C., Astor, Y., and Muller-Karger, F.: Radionuclide fluxes and particle scavenging in Cariaco Basin, Cont. Shelf Res., 24, 1451–1463, https://doi.org/10.1016/j.csr.2004.05.005, 2004.
Somayajulu, B. L. K., Rengarajan, R., and Jani, R. A.: Geochemical cycling in the Hooghly estuary, India, Mar. Chem., 79, 171–183, https://doi.org/10.1016/S0304-4203(02)00062-2, 2002.
Speicher, E. A., Moran, S. B., Burd, A. B., Delfanti, R., Kaberi, H., Kelly, R. P., Papucci, C., Smith, J. N., Stavrakakis, S., Torricelli, L., and Zervakis, V.: Particulate organic carbon export fluxes and size-fractionated POC/234Th ratios in the Ligurian, Tyrrhenian and Aegean Seas, Deep-Sea Res. Pt. I, 53, 1810–1830, https://doi.org/10.1016/j.dsr.2006.08.005, 2006.
Steinberg, D. K. and Landry, M. R.: Zooplankton and the Ocean Carbon Cycle, Ann. Rev. Mar. Sci., 9, 413–444, https://doi.org/10.1146/annurev-marine-010814-015924, 2017.
Stewart, G., Cochran, J. K., Miquel, J. C., Masqué, P., Szlosek, J., Rodriguez y Baena, A. M., Fowler, S. W., Gasser, B., and Hirschberg, D. J.: Comparing POC export from 234Th/238U and 210Po/210Pb disequilibria with estimates from sediment traps in the northwest Mediterranean, Deep-Sea Res. Pt. I, 54, 1549–1570, https://doi.org/10.1016/j.dsr.2007.06.005, 2007.
Stewart, G., Moran, S. B., Lomas, M. W., and Kelly, R. P.: Direct comparison of 210Po, 234Th and POC particle-size distributions and export fluxes at the Bermuda Atlantic Time-series Study (BATS) site, J. Environ. Radioact., 102, 479–489, https://doi.org/10.1016/j.jenvrad.2010.09.011, 2011.
Stukel, M. and California Current Ecosystem LTER: Total Thorium-234 (Th-234) taken from discrete water column samples collected during CCE Process Cruises (2006–2017). ver 4, Environmental Data Initiative, https://doi.org/10.6073/pasta/f124cdffb311eaf778519c873314ffdc, 2019.
Stukel, M. R., Landry, M. R., Benitez-Nelson, C. R., and Goericke, R.: Trophic cycling and carbon export relationships in the California current ecosystem, Limnol. Oceanogr., 56, 1866–1878, https://doi.org/10.4319/lo.2011.56.5.1866, 2011.
Stukel, M. R., Ohman, M. D., Benitez-Nelson, C. R., and Landry, M. R.: Contributions of mesozooplankton to vertical carbon export in a coastal upwelling system, Mar. Ecol. Prog. Ser., 491, 47–65, https://doi.org/10.3354/meps10453, 2013.
Stukel, M. R., Kahru, M., Benitez-Nelson, C. R., Décima, M., Goericke, R., Landry, M. R., and Ohman, M. D.: Using Lagrangian-based process studies to test satellite algorithms of vertical carbon flux in the eastern North Pacific Ocean, J. Geophys. Res.-Ocean., 120, 7208–7222, https://doi.org/10.1002/2015JC011264, 2015.
Stukel, M. R., Benitez-Nelson, C. R., Decima, M., Taylor, A. G., Buchwald, C., and Landry, M. R.: The biological pump in the Costa Rica Dome: An open-ocean upwelling system with high new production and low export, J. Plankton Res., 38, 348–365, https://doi.org/10.1093/plankt/fbv097, 2016.
Stukel, M. R., Aluwihare, L. I., Barbeau, K. A., Chekalyuk, A. M., Goericke, R., Miller, A. J., Ohman, M. D., Ruacho, A., Song, H., Stephens, B. M., and Landry, M. R.: Mesoscale ocean fronts enhance carbon export due to gravitational sinking and subduction, Proc. Natl. Acad. Sci. USA, 114, 1252–1257, https://doi.org/10.1073/pnas.1609435114, 2017.
Stukel, M. R., Kelly, T. B., Aluwihare, L. I., Barbeau, K. A., Goericke, R., Krause, J. W., Landry, M. R., and Ohman, M. D.: The Carbon:234Thorium ratios of sinking particles in the California current ecosystem 1: relationships with plankton ecosystem dynamics, Mar. Chem., 212, 1–15, https://doi.org/10.1016/j.marchem.2019.01.003, 2019.
Stumm, W.: Chemical interaction in particle separation, Environ. Sci. Technol., 11, 1066–1070, https://doi.org/10.1021/es60135a010, 1977.
Sweeney, E. N., McGillicuddy, D. J., and Buesseler, K. O.: Biogeochemical impacts due to mesoscale eddy activity in the Sargasso Sea as measured at the Bermuda Atlantic Time-series Study (BATS), Deep-Sea Res. Pt. II, 50, 3017–3039, https://doi.org/10.1016/j.dsr2.2003.07.008, 2003.
Szlosek, J., Cochran, J. K., Miquel, J. C., Masqué, P., Armstrong, R. A., Fowler, S. W., Gasser, B., and Hirschberg, D. J.: Particulate organic carbon–234Th relationships in particles separated by settling velocity in the northwest Mediterranean Sea, Deep-Sea Res. Pt. II, 56, 1519–1532, https://doi.org/10.1016/j.dsr2.2008.12.017, 2009.
Tanaka, N., Takeda, Y., and Tsunogai, S.: Biological effect on removal of Th-234, Po-210 and Pb-210 from surface water in Funka Bay, Japan, Geochim. Cosmochim. Ac., 47, 1783–1790, https://doi.org/10.1016/0016-7037(83)90026-1, 1983.
Thomalla, S., Turnewitsch, R., Lucas, M., and Poulton, A.: Particulate organic carbon export from the North and South Atlantic gyres: The 234Th/238U disequilibrium approach, Deep-Sea Res. Pt. II, 53, 1629–1648, https://doi.org/10.1016/j.dsr2.2006.05.018, 2006.
Thomalla, S. J.: Particulate organic carbon and mineral export from the North and South Atlantic gyres: the 234Th 238U disequilibrium approach, University of Cape Town, 2007.
Thomalla, S. J., Poulton, A. J., Sanders, R., Turnewitsch, R., Holligan, P. M., and Lucas, M. I.: Variable export fluxes and efficiencies for calcite, opal, and organic carbon in the Atlantic Ocean: A ballast effect in action?, Global Biogeochem. Cycles, 22, GB1010, https://doi.org/10.1029/2007GB002982, 2008.
Thomalla, S. J., Racault, M. F., Swart, S., and Monteiro, P. M. S.: High-resolution view of the spring bloom initiation and net community production in the Subantarctic Southern Ocean using glider data, ICES J. Mar. Sci., 72, 1999–2020, https://doi.org/10.1093/icesjms/fsv105, 2015.
Thunell, R. C., Moore, W. S., Dymond, J., and Pilskaln, C. H.: Elemental and isotopic fluxes in the Southern California Bight: a time-series sediment trap study in the San Pedro Basin, J. Geophys. Res., 99, 875–889, https://doi.org/10.1029/93JC02377, 1994.
Trimble, S. M. and Baskaran, M.: The role of suspended particulate matter in 234Th scavenging and 234Th-derived export fluxes of POC in the Canada Basin of the Arctic Ocean, Mar. Chem., 96, 1–19, https://doi.org/10.1016/j.marchem.2004.10.003, 2005.
Trimble, S. M., Baskaran, M., and Porcelli, D.: Scavenging of thorium isotopes in the Canada Basin of the Arctic Ocean, Earth Planet. Sc. Lett., 222, 915–932, https://doi.org/10.1016/j.epsl.2004.03.027, 2004.
Tsunogai, S., Minagawa, M., and Minagwa, M.: Vertical flux of organic materials estimated from Th-234 in the ocean., Jt. Oceanogr. Assem., 13–24, 156, 1976.
Tsunogai, S., Taguchi, K., and Harada, K.: Seasonal variation in the difference between observed and calculated particulate fluxes of Th-234 in Funka Bay, Japan, J. Oceanogr. Soc. Japan, 42, 91–98, https://doi.org/10.1007/BF02109095, 1986.
Turekian, K. K.: The fate of metals in the oceans, Geochim. Cosmochim. Ac., 41, 1139–1144, https://doi.org/10.1016/0016-7037(77)90109-0, 1977.
Turner, J. T.: Zooplankton fecal pellets, marine snow and sinking phytoplankton blooms, Aquat. Microb. Ecol., 27, 57–102, https://doi.org/10.3354/ame027057, 2002.
Turnewitsch, R.: Thorium 234 in bottom water at station M42/2_411-8, Pangaea, https://doi.org/10.1594/PANGAEA.58833, 2001.
Turnewitsch, R. and Springer, B. M.: Do bottom mixed layers influence 234Th dynamics in the abyssal near-bottom water column?, Deep-Sea Res. Pt. I, 48, 1279–1307, https://doi.org/10.1016/S0967-0637(00)00104-7, 2001.
Turnewitsch, R., Reyss, J. L., Nycander, J., Waniek, J. J., and Lampitt, R. S.: Internal tides and sediment dynamics in the deep sea-Evidence from radioactive 234Th/238U disequilibria, Deep-Sea Res. Pt. I, 55, 1727–1747, https://doi.org/10.1016/j.dsr.2008.07.008, 2008.
Turnewitsch, R., Dumont, M., Kiriakoulakis, K., Legg, S., Mohn, C., Peine, F., and Wolff, G.: Tidal influence on particulate organic carbon export fluxes around a tall seamount, Prog. Oceanogr., 149, 189–213, https://doi.org/10.1016/j.pocean.2016.10.009, 2016.
Umhau, B. P., Benitez-Nelson, C. R., Close, H. G., Hannides, C. C. S., Motta, L., Popp, B. N., Blum, J. D.. and Drazen, J. C.: Seasonal and spatial changes in carbon and nitrogen fluxes estimated using 234Th:238U disequilibria in the North Pacific tropical and subtropical gyre, Mar. Chem., 217, 103705, https://doi.org/10.1016/j.marchem.2019.103705, 2019.
Usbeck, R., Rutgers van der Loeff, M., Hoppema, M.. and Schlitzer, R.: Shallow remineralization in the Weddell Gyre, Geochem. Geophys. Geosyst., 3, 1–18, https://doi.org/10.1029/2001gc000182, 2002.
Villa-Alfageme, M., de Soto, F. C., Ceballos, E., Giering, S. L. C., Le Moigne, F. A. C., Henson, S., Mas, J. L., and Sanders, R. J.: Geographical, seasonal, and depth variation in sinking particle speeds in the North Atlantic, Geophys. Res. Lett., 43, 8609–8616, https://doi.org/10.1002/2016GL069233, 2016.
Villa-Alfageme, M., Briggs, N., Ceballos-Romero, E., de Soto, F., Manno, C., and Giering, S. L.: Seasonal variations of sinking velocities in Austral diatom blooms: Lessons learned from COMICS I, Deep-Sea Res. Pt. II, in review, 2021.
Volk, T. and Hoffert, M. I.: Ocean carbon pumps: analysis of relative strengths and efficiencies in ocean-driven atmospheric CO2 changes., in The carbon cycle and atmospheric CO, American Geophysical Union, 99–110, 1985.
Waples, J. T., Orlandini, K. A., Edgington, D. N. and Klump, J. V.: Seasonal and spatial dynamics of 234Th/238U disequilibria in southern Lake Michigan, J. Geophys. Res.-Ocean., 109, C10S06, https://doi.org/10.1029/2003JC002204, 2004.
Waples, J. T., Benitez-Nelson, C., Savoye, N., Rutgers van der Loeff, M., Baskaran, M. and Gustafsson, Ö.: An introduction to the application and future use of 234Th in aquatic systems, Mar. Chem., 100, 166–189, https://doi.org/10.1016/j.marchem.2005.10.011, 2006.
Wei, C. L. and Hung, C. C.: Particle scavenging in the upper water column off Mindoro Island, Philippine: 234Th/238U disequilibria, Estuar. Coast. Shelf Sci., 46, 351–358, https://doi.org/10.1006/ecss.1997.0297, 1998.
Wei, C.-L. and Murray, J. W.: 234Th/238U disequilibria in the Black Sea, Deep-Sea Res. Pt. I, S855–S873, https://doi.org/10.1016/s0198-0149(10)80013-5, 1991.
Wei, C. L. and Murray, J. W.: Temporal variations of 234Th activity in the water column of Dabob Bay: Particle scavenging, Limnol. Oceanogr., 37, 296–314, https://doi.org/10.4319/lo.1992.37.2.0296, 1992.
Wei, C.-L., Chou, L., Tsai, J., Wen, L., and Pai, S.: Comparative Geochemistry of 234Th, 210Pb, and 210Po: A Case Study in the Hung-Tsai Trough off Southwestern Taiwan, Terr. Atmos. Ocean. Sci., 20, 411, https://doi.org/10.3319/TAO.2008.01.09.01(Oc), 2009.
Wei, C.-L., Lin, S.-Y., Sheu, D. D.-D., Chou, W.-C., Yi, M.-C., Santschi, P. H., and Wen, L.-S.: Particle-reactive radionuclides (234Th, 210Pb, 210Po) as tracers for the estimation of export production in the South China Sea, Biogeosciences, 8, 3793–3808, https://doi.org/10.5194/bg-8-3793-2011, 2011.
Weinstein, S. E. and Moran, S. B.: Vertical flux of particulate Al, Fe, Pb, and Ba from the upper ocean estimated from 234Th/238U disequilibria, Deep-Sea Res. Pt. I, 52, 1477–1488, https://doi.org/10.1016/j.dsr.2005.03.008, 2005.
Xie, R. C., Le Moigne, F. A. C., Rapp, I., Lüdke, J., Gasser, B., Dengler, M., Liebetrau, V., and Achterberg, E. P.: Effects of 238U variability and physical transport on water column 234Th downward fluxes in the coastal upwelling system off Peru, Biogeosciences, 17, 4919–4936, https://doi.org/10.5194/bg-17-4919-2020, 2020.
Xu, C., Santschi, P. H., Hung, C. C., Zhang, S., Schwehr, K. A., Roberts, K. A., Guo, L., Gong, G. C., Quigg, A., Long, R. A., Pinckney, J. L., Duan, S., Amon, R., and Wei, C. L.: Controls of 234Th removal from the oligotrophic ocean by polyuronic acids and modification by microbial activity, Mar. Chem., 123, 111–126, https://doi.org/10.1016/j.marchem.2010.10.005, 2011.
Yang, Y., Han, X., and Kusakabe, M.: POC fluxes from euphotic zone estimated from234Th deficiency in winter in the northwestern North Pacific Ocean, Acta Oceanol. Sin., 23, 135–148, 2004.
Yebra, L., Herrera, I., Mercado, J. M., Cortés, D., Gómez-Jakobsen, F., Alonso, A., Sánchez, A., Salles, S., and Valcárcel-Pérez, N.: Zooplankton production and carbon export flux in the western Alboran Sea gyre (SW Mediterranean), Prog. Oceanogr., 167, 64–77, https://doi.org/10.1016/j.pocean.2018.07.009, 2018.
Yool, A., Martin, A. P., Fernández, C., and Clark, D. R.: The significance of nitrification for oceanic new production, Nature, 447, 999–1002, https://doi.org/10.1038/nature05885, 2007.
Yu, W., Chen, L., Cheng, J., He, J., Yin, M., and Zeng, Z.: 234Th-derived particulate organic carbon export flux in the western Arctic Ocean, Chinese J. Oceanol. Limnol., 28, 1146–1151, https://doi.org/10.1007/s00343-010-9933-1, 2010.
Yu, W., He, J., Li, Y., Lin, W., and Chen, L.: Particulate organic carbon export fluxes and validation of steady state model of 234Th export in the Chukchi Sea, Deep-Sea Res. Pt. II, 81–84, 63–71, https://doi.org/10.1016/j.dsr2.2012.03.003, 2012.
Zhou, K., Nodder, S. D., Dai, M., and Hall, J. A.: Insignificant enhancement of export flux in the highly productive subtropical front, east of New Zealand: a high resolution study of particle export fluxes based on 234Th: 238U disequilibria, Biogeosciences, 9, 973–992, https://doi.org/10.5194/bg-9-973-2012, 2012.
Zhou, K., Dai, M., Kao, S. J., Wang, L., Xiu, P., Chai, F., Tian, J., and Liu, Y.: Apparent enhancement of 234Th-based particle export associated with anticyclonic eddies, Earth Planet. Sc. Lett., 381, 198–209, https://doi.org/10.1016/j.epsl.2013.07.039, 2013.
Zhou, K., Maiti, K., Dai, M., Kao, S. J., and Buesseler, K.: Does adsorption of dissolved organic carbon and thorium onto membrane filters affect the carbon to thorium ratios, a primary parameter in estimating export carbon flux?, Mar. Chem., 184, 1–10, https://doi.org/10.1016/j.marchem.2016.06.004, 2016.